Justice EID
delivered the Opinion of the Court.
We issued a rule to show cause to consider whether the trial court erred by declaring a mistrial when the jury failed to return a verdict on the charge of first-degree murder against Defendant Marvin Richardson. Richardson argues that the mistrial was not manifestly necessary as to the offenses of first- and second-degree murder because the jury unanimously agreed he was not guilty of those offenses and the jury was deadlocked only as to the lesser-included offenses of manslaughter and criminally negligent homicide. Richardson further argues that the trial court should have conducted a partial verdict inquiry before declaring a mistrial, and he offers affidavits from the jurors to support his claim that had a partial verdict inquiry been conducted, the jury would have acquitted him of the offenses of first- and second-degree murder.
We now hold that a mistrial was manifestly necessary because the jury was deadlocked as to the first-degree murder charge. Consequently, double jeopardy does not bar retrial of Richardson on the first-degree murder charge or its lesser-included offenses of second-degree murder, manslaughter, and criminally negligent homicide. We further hold that the trial court properly refused Richardson's requests to poll the jury as to the offenses of first- and second-degree murder and to consider the jurors' affidavits as [758]*758evidence of a partial verdict. We therefore discharge the rule to show cause.
I.
While driving a pickup truck on September 11, 2005, Richardson struck and killed his cousin, Ricky Smith. As a result, Richardson was ultimately charged with first-degree murder, vehicular homicide (DUI), and vehicular homicide (reckless). All three charges were submitted to the jury, and lesser-included offenses were also submitted with two of the charges. In particular, the lesser-included offenses of second-degree murder, manslaughter, and criminally negligent homicide were submitted with the first-degree murder charge; and the lesser-included offense of careless driving resulting in death was submitted with the vehicular homicide (reckless) charge.
The jury received three verdict forms, one for each charge. The forms containing lesser-included offenses followed the format recommended by the Colorado Jury Instructions, CJI-Crim. 88:07. The relevant portion of the form for first-degree murder reads as follows:
JURY VERDICT
CHARGE OF MURDER IN THE FIRST-DEGREE
I.* We, the jury, find the Defendant, MARVIN RICHARDSON, NOT GUILTY of Murder in the First-degree and the lesser included offenses of Murder in the Second-degree, Manslaughter and Criminally Negligent Homicide against Ricky Smith.
Foreperson
II.* We, the jury, find the Defendant, MARVIN RICHARDSON, GUILTY of;
* *[ ] Murder in the First-degree
* *[] Murder in the Second-degree* ok
* *[ ] Manslaughter
* *[ ] Criminally Negligent Homicide
Foreperson
*The Foreperson should sign only one of the above (I or II). If the verdiet is NOT GUILTY, then I above should be signed. If the verdict is GUILTY, then II above should be signed.
**If you find the Defendant guilty of the crime charged or one of the lesser included offenses the foreman must complete this GUILTY verdict by placing, in ink, an "X" in the appropriate square. ONLY ONE SQUARE may be filled in, with the remainder to remain unmarked.
Thus, while the form permitted the jury to find Richardson not guilty on first-degree murder and the lesser-included offenses of second-degree murder, manslaughter, and criminally negligent homicide as a collective matter, there was no place on the form for the jury to return a not-guilty verdict on first-degree murder, second-degree murder, manslaughter, or criminally negligent homicide as an individual matter. The only individual consideration appeared in the guilty portion of the form, which allowed the jury to find Richardson guilty of first-degree murder, second-degree murder, manslaughter, or criminally negligent homicide. Nothing in the record indicates that Richardson objected to structuring the first-degree murder verdict form in this way.
The jury began deliberations on Tuesday, March 6, 2007. On Friday, March 9th, the jury sent the trial court a note asking, "How long do we continue to deliberate without coming to a consensus? At what point do we become a hung jury?" The court answered, "You should continue to deliberate so long as progress is being made toward a unanimous verdict." Richardson objected to this answer, arguing that the jury should be told it is not a hung jury if the jurors have reached unanimity on any count. The court overruled the objection, stating, "I've not interpreted the question to mean that [the jury has] reached unanimity of anything.... It's simply an inquiry from the jury about what's next and how long should we try."
Later the same day, the jury asked for and received permission to go home for the weekend. The trial court denied Richardson's request for the court to inquire, under People v. Lewis, 676 P.2d 682 (Colo.1984), whether [759]*759the jury was making any progress toward a unanimous verdict, and if not, whether the jury was divided over Richardson's guilt or innocence as to one of the charges, or whether the division only concerned Richardson's degree of guilt. The court based its decision on its conclusion that "[the jury has not expressed any indication that they are a hung jury."
Deliberations resumed the following Monday, March 12th, and the jury sent a note asking, "If we have reached consensus regarding a particular charge but have some people who think the defendant is guilty of a higher charge have we reached unanimity regarding the lesser charge according to the law?" Richardson requested that the trial court provide the following instruction:
You should return a guilty verdict on any lesser included offense, only if all jurors unanimously agree on the defendant's guilt as to the lesser included offense and no juror remains convinced beyond a reasonable doubt by the facts and law that the defendant is guilty of a greater offense submitted for the jury's consideration.
The People, however, objected to this instruction on the ground that it was barred by section 18-1-408(8), C.R.S. (2007),1 because it instructed the jury to convict on a lesser-included offense.
The trial court agreed with the People, stating:
The Court believes that 18-1-408@8) is mandatory in its language and that it prevents the Court from instructing the jury further regarding reaching a consensus on the guilt of the defendant on a lesser charge so long as there is a remaining juror who believes the defendant is guilty of a greater offense and that if the prosecution wishes to prevent any other inquiry of the jury as to lesser included offense, that that statute entitles them to do that.
Instead of giving the jury Richardson's proposed instruction, the court provided the following answer to the jury's question: "If any juror remains convinced by the facts and law that the defendant is guilty of a greater offense, then the jury has not reached unanimity. You should continue to deliberate if there is a likelihood of progress toward a unanimous verdiet on any charge."
The jury subsequently sent a note announcing that they had reached a unanimous decision on one charge, but that they had stopped making progress toward a unanimous decision on the other two charges. At this point, Richardson requested that the trial court instruct the jury to return a verdict on any greater-included or lesser-included offense as to which they had reached unanimity. The court declined this request and accepted three verdict forms from the jury. The form for vehicular homicide (DUI) was signed and found Richardson not guilty. However, the forms for first-degree murder and vehicular homicide (reckless) were unsigned and unmarked.
Richardson requested the trial court to poll the jury as to their unanimity on the charge of first-degree murder and the lesser-included offense of second-degree murder, but the court refused. The court acknowledged that the jury had returned a verdict solely on the charge of vehicular manslaughter (DUI) and asked each juror, "Is this your verdict?" Each juror replied "yes," and the court dismissed the jury. The court then denied Richardson's second request to poll the jury. The court also discussed the need to set a date for retrial, and eventually scheduled a hearing to conduct further proceedings and set the retrial date. Although it did not expressly declare a mistrial at that time, the court's order dated March 14, 2007, stated that the jury had "failed to reach a verdict as to Counts One and Three" and that "[the Court declared a mistrial and will proceed to set the case for retrial within 90 days of [March 12, 2007]."
Richardson subsequently hired investigators to interview the jurors. The investigators obtained affidavits from all twelve jurors stating that the jury had unanimously agreed [760]*760that Richardson was not guilty of first- or second-degree murder. Based on the affidavits, Richardson moved to dismiss these charges on double jeopardy grounds. The People stipulated to the affidavits for purposes of the motion only, but argued that CRE 606(b)2 prohibited the court from considering them. The trial court agreed and denied Richardson's motion. We issued a rule to show cause.
IL
The overarching issue in this case is whether the first- and second-degree murder charges against Richardson should be dismissed. Richardson argues that double jeopardy bars a retrial on those charges because there was no manifest necessity for a mistrial. Richardson also argues that the jurors' affidavits should be considered in addressing his double jeopardy claim. We consider each argument in turn.
A.
"Double jeopardy is a constitutional guarantee prohibiting the retrial of a defendant who already has been tried for the same offense." People v. Berreth, 13 P.3d 1214, 1216 (Colo.2000). One principle of double jeopardy is that the defendant "is entitled to have his trial completed by a particular tribunal." People v. Schwartz, 678 P.2d 1000, 1011 (Colo.1984). However, a mistrial may be declared if manifestly necessary, and the defendant may then be subject to a second trial. Id.; accord Berreth, 13 P.3d at 1216. The existence of manifest necessity depends on the cireumstances of the case. Berreth, 13 P.3d at 1216-17; Schwartz, 678 P.2d at 1011. Jury deadlock is one circumstance that may warrant a mistrial. Berreth 13 P.3d at 1217; Schwartz, 678 P2d at 1011; see also § 18-1-801(2)(b)(IV), C.R.S. (2007) (The trial court may declare a mistrial if it finds that "[the jury is unable to agree upon a verdict."). In order for a mistrial to be manifestly necessary, "the jury must actually be unable to reach a verdict." Schwartz, 678 P.2d at 1011. This determination lies within the trial court's discretion. Id. When dealing with a deadlocked jury, the trial court "should employ all legal and reasonable measures to secure a verdict," but it must also take care to avoid "the coercion of verdicts by improper ... influence." Barriner v. Dist. Court, 174 Colo. 447, 453, 484 P.2d 774, 776 (1971) (citation and quotation omitted).
We begin by determining whether the trial court did in fact declare a mistrial due to jury deadlock as to the charge of first-degree murder. When the jury returned the three verdict forms, the court did not expressly declare a mistrial. However, with respect to the first-degree murder charge, the court did acknowledge that the jury had failed to return a signed verdict form and that a retrial would be necessary. The parties and the court then discussed possible dates for a retrial. Two days later, the court issued an order stating that a mistrial had been declared. Although the court did not expressly declare a mistrial at the time the jury returned the unsigned verdict form, the record in this case shows that the court and the parties understood that a mistrial had been declared. We therefore conclude that the trial court did in fact declare a mistrial based on jury deadlock as to the charge of first-degree murder.
Our next inquiry is whether the mistrial was manifestly necessary-that is, whether the jury was actually unable to reach a verdict on the charge of first-degree murder. As the verdict form indicated, the jury had two options: (1) acquit Richardson of first-degree murder and all lesser-included [761]*761offenses, or (2) convict him for either first-degree murder or one of the lesser-included offenses. Unanimity was required as to either option. See Crim. P. 28(a)(8), 8l1(a)(8); see also § 18-1-406(1), C.R.S. (2007). However, the jury's questions on Friday, March 9th and Monday, March 12th indicated that no unanimity had been reached as to either option. Although all jurors agreed Richardson was guilty of some homicide offense (preventing unanimity on option 1), they disagreed over the particular offense (preventing unanimity on option 2). In other words, the jury was deadlocked3 as to the degree of Richardson's guilt.
In People v. Lewis, we addressed the issue of how a trial court should handle a jury that is deadlocked as to the degree of guilt. 676 P.2d 682 (Colo.1984). There, we gave trial courts the following guidance:
The court should first ask the jury whether there is a likelihood of progress towards a unanimous verdict upon further deliberation. An affirmative response should require further deliberation without any additional instruction. If the jury indicates that the deadlock is such that progress towards a unanimous verdict is unlikely, the court should then inquire whether the jury is divided over guilt as to any one of the offenses and nonguilt as to all offenses, or instead, whether the division centers only on the particular degree of guilt. In the event the jury impasse relates solely to the issue of guilt as to any one of the offenses and nonguilt as to all offenses, the court in its discretion may give Colo. J.I. (Crim.) 38:14 (1988), which is patterned after ABA Standards for Criminal Justice 15-44 (2d ed.1980) and the 1971 directive of the Chief Justice. If, however, the jury deadlock centers solely on a particular degree of guilt, rather than on the issue of guilt or nonguilt, then the court should consider an additional instruction charging the jury to return a guilty verdict on the lesser offense as long as every essential element of the lesser offense is necessarily included in the greater offense and all jurors unanimously agree on the defendant's guilt as to either the lesser or greater offenses submilted to them for their consideration.
Lewis, 676 P.2d at 689 (footnotes omitted) (emphasis added). However, Lewis instructions are not constitutionally required, and instead, are left to the discretion of the trial court. See id. (offering "guidelines" for dealing with deadlocked juries); People v. Barnard, 12 P.3d 290, 295 (Colo.App.2000) ("[The giving of [a Lewis ] instruction is not mandatory.").
Sixteen years after our decision in Lewis, the General Assembly added subsection (8) to section 18-1-408, C.R.S. ("Prosecution of multiple counts for same act."). See Ch. 131, see. 5, § 18-1-408, 2000 Colo. Sess. Laws 451, 458. Subsection (8) states:
Without the consent of the prosecution, no jury shall be instructed to return a guilty verdict on a lesser offense if any juror remains convinced by the facts and law that the defendant is guilty of a gr:ater offense submitted for the jury's consideration, the retrial of which would be barred by conviction of the lesser offense.
§ 18-1-408(8) (emphasis added).
Contrary to Lewis's guidelines, seetion 18-1-408(8) expressly prohibits the trial court from alleviating jury deadlock over the degree of guilt by instructing the jury, without the prosecution's consent, to return a guilty verdict on a lesser-included offense. Rather, if any jwror remains convinced by the facts and the law that the defendant is guilty of a greater offense, the jury cannot be instructed, without the prosecution's consent, to return a verdict on a lesser-included offense. Because Lewis instructions are not constitutionally required, the General Assembly may prohibit or alter them. Therefore, we hold that section 18-1-408(8) abrogates the part of Lewis that allows the trial court to instruct the jury, without the prosecution's consent, to return a guilty verdict on a lesser-included offense if the jury has reached [762]*762consensus as to the defendant's guilt but is deadlocked as to the degree of guilt.
In light of our interpretation of seetion 18-1-408(8), we conclude that the trial court's responses to the jury's questions were proper. On the fourth day of deliberations, the jury asked how long they should continue to deliberate, and in keeping with Lewis, the trial court properly instructed the jury to "continue to deliberate so long as progress is being made toward a unanimous verdict." See Lewis 676 P.2d at 689 ("The court should first ask the jury whether there is a likelihood of progress towards a unanimous verdict upon further deliberation."). On the fifth day of deliberations, the jury indicated they were deadlocked as to the degree of Richardson's guilt. As section 18-1-408(8) requires, the trial court told the jury, "If any juror remains convinced by the facts and law that the defendant is guilty of a greater offense, then the jury has not reached unanimity. You should continue to deliberate if there is a likelihood of progress toward a unanimous verdict on any charge." 4
Later that afternoon, the jury indicated that they had reached a unanimous verdict on only one charge and that they were not making progress toward unanimity on the other two charges, one of which was first-degree murder. The trial court then accepted all three verdict forms and dismissed the jury. Under these circumstances, we hold that a mistrial as to the first-degree murder charge was manifestly necessary because the jury was actually unable to reach a verdict on that charge. See Schwartz, 678 P.2d at 1012 (affirming a mistrial declared after the trial court properly refused to give the defendant's requested instruction to a deadlocked Jury).
Consequently, double jeopardy does not bar retrial of Richardson on the charge of first-degree murder. Because the lesser-included offenses are considered the same as the greater offense for purposes of double jeopardy, People v. Moore, 877 P.2d 840, 844 (Colo.1994), on retrial the first-degree murder charge against Richardson may include the lesser offenses of second-degree murder, manslaughter, and criminally negligent homicide.
B.
As noted above, section 18-1-408(8) prevents the jury from being instructed, without the prosecution's consent, to return a verdict on a lesser-included offense if any juror remains convinced that the defendant is guilty of a greater offense. However, it does not prevent a jury from being presented with a verdict form that gives jurors the option of considering the charge and its lesser-inelud-ed offenses on an individual basis, and acquitting the defendant on some or all of them. In other words, the verdict form that was given to the jury in this case-which allowed the jurors to return a not guilty verdict only if they found Richardson not guilty of first-degree murder, second-degree murder, manslaughter, and criminally negligent homicide-was not required by section 18-1-408(8). Nevertheless, Richardson did not object to the jury verdict form at trial, and does not directly challenge it before us on appeal.
Richardson does, however, challenge the verdiet form indirectly by arguing that the jurors should have been given an opportunity to convey their conclusions with regard to the greater offense and lesser-included offenses through either (1) polling by the trial court, or (2) by juror affidavits. Richardson argues that the juror affidavits show, and polling by the trial court would have shown, that the jurors had reached unanimity on the first- and second-degree murder charges and would have acquitted him on those charges. He argues that double jeopardy therefore bars retrial on those charges. We consider [763]*763Richardson's arguments based on jury polling and juror affidavits, and ultimately reject them both.
1.
When Richardson asked the trial court to poll the jury when it returned the unsigned first-degree murder verdiet form, he was essentially asking the court to conduct a partial verdict inquiry,5 which Richardson believed would acquit him of the greater two of the four homicide offenses e., first- and second-degree murder). Several other jurisdictions have addressed this issue, and the majority has held that if a single charge includes multiple degrees of offenses, the trial court may not conduct a partial verdiet inquiry as to the offenses included within the charge. See, e.g., People v. Flail, 25 Ill.App.3d 992, 824 N.E.2d 50, 52-53 (1975); State v. Bell, 322 N.W.2d 93, 95 (Iowa 1982); State v. McKay, 217 Kan. 11, 535 P.2d 945, 947 (1975); Commonwealth v. Roth, 437 Mass. 777, 776 N.E.2d 487, 450 (2002); People v. Hickey, 103 Mich.App. 850, 303 N.W.2d 19, 21 (1981); State v. Booker, 306 N.C. 302, 293 S.E.2d 78, 80 (1982). The minority, on the other hand, has held that double jeopardy requires a partial verdict of acquittal as to the greater offenses if the jury is deadlocked only as to the lesser offenses.6 See, e.g., Whiteaker v. State, 808 P.2d 270, 278 (Alaska Ct.App.1991); Stone v. Superior Court, 31 503, 183 Cal.Rptr. 647, 646 P.2d 809, 820 (1982); State v. Tate, 256 Conn. 262, 773 A.2d 308, 321 (2001); State v. Pugliese, 120 N.H. 728, 422 A.2d 1319, 1321 (1980).
Commonwealth v. Roth exemplifies the majority rule. In Roth, the Massachusetts Supreme Court held "that judges should not initiate any inquiry into partial verdicts premised on lesser included offenses within a single complaint or count of an indictment." 776 N.E.2d at 450. The court first concluded that the Massachusetts Rules of Criminal Procedure do not permit partial verdicts and then moved to the question of whether double jeopardy nevertheless requires such verdicts. Id. at 445-46. The court began its double jeopardy analysis by acknowledging that partial verdict inquiries carry "significant potential for coercion" and that "deadlocked juries are particularly susceptible to coercion." Id. at 447. The court then elaborated on the coercion problem:
[The import of the [partial verdict] inquiry is unmistakable: "Can't you at least decide a part of this case?" The inquiry, by its nature, plays on the deadlocked jurors' natural sense of frustration, disappointment, and failure. The jurors are confronted with the request, and asked to absorb its inherent complexity, at the worst possible time, when they are tired, anxious to be discharged, and perhaps angry at fellow jurors whom they blame for failing to reach agreement. While technically inquiring only as to what the jurors have already agreed on, the request for partial verdiets broken down by lesser included offenses implicitly suggests that the jurors should try just a little bit harder to come back with at least a partial decision to show for all of their efforts.
Id. at 448.
The second problem the Roth court identified is the propensity of jurors to compromise in an attempt to reach a final verdict. In particular, the court noted that "a judge's request that the jury divulge the substance of their 'final vote may force the jury to report as 'final some votes that were not intended to be 'final unless they resolved the entire case." Id. at 448-49. For these reasons, the court concluded that double jeopardy does not require partial verdiet inquiries.
We find the Roth court's reasoning-including its concerns about juror coercion and compromise-persuasive. First, in the case where a jury has not completed deliberations [764]*764at the time of the partial verdict instruction, the resulting verdict might well be the result of juror eoercion-a particular concern where, as here, the jury is deadlocked. "For all the reasons that we would lack confidence in any verdict of guilty that was returned under such conditions, we should lack confidence in any verdict of not guilty." Roth, 776 N.E.2d at 448; see also Lewis, 676 P.2d at 686 ("Unanimity requires a free and untrammeled deliberative process that expresses the conscientious conviction of each individual juror.").
Second, a jury's deliberations should not be given the legal force of a final verdict until the end result is expressed on a verdiet form returned in open court as required by Colorado law. See § 16-10-108, C.R.S. (2007); Crim. P. 28(a)(8); see also Hickey, 303 N.W.2d at 21 ("[The weight of final adjudication should not be given to any jury action that is not returned in a final verdict."); Booker, 298 S.E.2d at 80 ("[The better reasoned rule is the majority rule which requires a final verdict ...."). Indeed, it is very possible that jurors could believe that a defendant is guilty of a greater charge, but focus on lesser offenses "in a spirit of compromise to reach a verdict." Hall, 324 N.E.2d at 52; see also Hickey, 303 N.W.2d at 21 ("[Als a practical matter ... jury votes on included offenses may be the result of a temporary compromise in an effort to reach unanimity."). Moreover, under the verdict form used in this case, "the jury was to return a single verdict," not separate not-guilty verdiets on each of the greater and lesser offenses. Bell, 322 N.W.2d at 95. In short, the jury's informal and non-final discussions and decisions concerning the first- and second-degree murder charges against Richardson are not reliable. See Roth, 776 N.E.2d at 448 (discussing the unreliability of jury deliberations "until there is a final verdict on the entire charge"). Therefore, the trial court properly accepted the jury's final verdict and properly refused to poll the jurors with regard to interim votes on the first- and second-degree murder charges.7
2.
We also reject Richardson's argument that the jurors' affidavits should be considered in addressing his double jeopardy claim. We recently addressed this issue in Stewart v. Rice, where we determined that CRE 606(b) "broadly prohibits using juror testimony to contest a verdict." 47 P.3d 316, 321 (Colo.2002). Richardson, however, argues that the affidavits are admissible under an exception to CRE 606(b). In Stewart, we held that juror affidavits are only admissible to show that (1) extraneous prejudicial information was improperly brought to the jurors' attention, (2) a juror was improperly affected by an outside influence, or (8) the verdict contains a clerical error. Id. at 323-24. None of these exceptions applies here because Richardson offers the affidavits as evidence of the jury's deliberations for the purpose of impeaching the final verdict that was returned in open court, and this use is prohibited. Id. at 828 (stating that jurors may not impeach a verdict by testifying about their deliberations). Therefore, the affidavits are not admissible under CRE 606(b).
Richardson attempts to avoid CRE 606(b) altogether by arguing alternatively that the rule is inapplicable because the jury never returned a verdict on the first-degree murder charge. In other words, Richardson ar[765]*765gues that CRE 606(b) does not apply because he is not challenging the validity of a verdict, but rather is attempting to establish what the verdiet was in the first place. See CRE 606(b) (stating that jurors may not testify an inquiry into the validity of a verdict" (emphasis added)).
We have never considered whether CRE 606(b) applies when a defendant seeks to establish a verdiect-in whole or in part-as to a charge on which the jury hung, and we need not do so today. Assuming the rule does apply, the jurors' affidavits are not admissible under any of its exceptions. Assuming the rule does not apply, the affidavits are still inadmissible because Colorado does not allow verdict by affidavit. Rather, under Colorado's criminal procedure rules, a verdict must be submitted on a signed verdict form that is returned in open court with an opportunity for each juror to be individually polled. See Crim. P. 81; see also § 16-10-108. Either way, the affidavits are not proper evidence for consideration in this case.
IIL.
In sum, we hold that a mistrial was manifestly necessary because the jury was deadlocked as to the first-degree murder charge. Consequently, double jeopardy does not bar retrial of Richardson on the first-degree murder charge or its lesser-included offenses of second-degree murder, manslaughter, and criminally negligent homicide. We further hold that the trial court properly refused Richardson's requests to poll the jury as to the offenses of first- and second-degree murder and to consider the jurors' affidavits as evidence of a partial verdict. We therefore discharge the rule to show cause.
Justice MARTINEZ dissents.
Justice BENDER does not participate.