People v. Tunis

2013 COA 161, 318 P.3d 524, 2013 WL 6461467, 2013 Colo. App. LEXIS 1868
CourtColorado Court of Appeals
DecidedDecember 5, 2013
DocketCourt of Appeals No. 09CA0593
StatusPublished
Cited by6 cases

This text of 2013 COA 161 (People v. Tunis) is published on Counsel Stack Legal Research, covering Colorado Court of Appeals primary law. Counsel Stack provides free access to over 12 million legal documents including statutes, case law, regulations, and constitutions.

Bluebook
People v. Tunis, 2013 COA 161, 318 P.3d 524, 2013 WL 6461467, 2013 Colo. App. LEXIS 1868 (Colo. Ct. App. 2013).

Opinion

Opinion by

JUDGE WEBB

T1 The victim in this criminal case was sexually assaulted in her home. Defendant, William Anthony Tunis, was charged with the offense and, at a subsequent jury trial, he was identified as the assailant based on the victim's testimony and DNA evidence, including Y Chromosome-Short Tandem Repeat (Y-STR) evidence. Defendant was ultimately convicted of sexual assault and second degree burglary, both class three felonies, and sentenced to the Department of Corree-tions for an indeterminate term of twelve years to life. His sentence included a determination that he qualified as a sexually violent predator.

12 Defendant appeals from the judgment of conviction and sentence, challenging, as an issue of first impression, the reliability of the Y-STR evidence. We affirm the judgment, but conclude that the sexually violent predator portion of defendant's sentence must be vacated.

I. Y-STR Evidence

13 For three reasons, defendant contends that the Y-STR evidence, which was admitted through expert testimony, was unreliable and the trial court therefore erred by admitting it. "We review a trial court's admission of expert testimony for an abuse of discretion and will reverse only when that decision is manifestly erroneous." People v. Rector, 248 P.3d 1196, 1200 (Colo.2011) (citing People v. Ramirez, 155 P.3d 371, 380 (Colo.2007)). We disagree with defendant and conclude that the trial court did not abuse its discretion.

A. Y-STR Analysis Generally

4 The following was not disputed at trial:

T5 Every person has a unique genetic code. This code consists of a unique pattern of DNA on the twenty-three pairs of chromo[527]*527somes that all humans have. Twenty-two of these pairs, called autosomes, are not sex-determinative. A mother and father contribute equally, and randomly, to the composition of their offspring's autosomes.

1 6 However, the last pair of chromosomes determines the offspring's sex, and are called sex chromosomes. In females this pair consists of two X chromosomes, while in males this pair consists of one X and one Y chromosome. Because females carry no Y chromosome, a male's entire Y chromosome comes from his father. Therefore, excluding consideration of very small changes due to random mutation, a male's Y chromosome contains the same DNA and genetic code as all members of his male lineage.

T 7 Traditional forensic DNA analysis identifies individuals by looking for specific types of DNA at specific locations across the twenty-two pairs of autosomes. Analysts can compare a suspect's DNA type at a specific location on a chromosome to the DNA type at the same location on the same chromosome from a crime scene sample If the types match, the DNA in the sample may have come from the suspect.

18 Analysts can obtain a more accurate match by executing this comparison for many different DNA types at different locations on different chromosomes. Because autosomes contain a random combination of DNA from an individual's mother and father, and discrete DNA types at different locations are inherited independently of one another, the accuracy of the identification increases exponentially when analysts find a DNA type match at more than one location. This statistical analysis is called the product rule because the probability of a match at one location is multiplied by the probability of a match at another location, and so on, resulting in an astronomically small probability that a random person's overall DNA profile would match the profile observed in the sample and the suspect.

11 9 The physical process and methodology of Y-STR analysis is the same as that of traditional forensic DNA analysis. In both cases, the same techniques allow analysts, using one of several kits manufactured by private companies, to compare DNA types at specific locations. However, Y-STR analysis only examines DNA types on the Y chromosome. Because the Y chromosome passes from father to son largely unchanged, the DNA types at different locations on the Y chromosomes are not inherited independently of one another. Therefore, the product rule is inapplicable.

T 10 Instead of the product rule, analysts use what is known as the counting method in Y-STR analysis. Analysts assemble a Y chromosome profile from DNA found in a crime scene sample by identifying different DNA types at specific locations on the Y chromosome. If the profile from the sample matches the suspect's Y chromosome profile, he and his paternal relatives cannot be ruled out as the source of the sample. Analysts then search for the same DNA profile in a database of several thousand individuals' profiles. Based on the number of individuals in the database who share that profile, analysts can then calculate what portion of the general population shares that profile In other words, if the matching profile occurs at a rate of 5% in the database, about 95% of the population represented by that database can be excluded as the source of the sample.

B. Governing Law

1 11 The admissibility of scientific evidence in Colorado is governed by CRE 702 and 403. People v. Shreck, 22 P.3d 68, 78 (Colo.2001).

112 CRE 702 requires the scientific evidence be both reliable and relevant. See id. at T7. "In determining whether the [scientific] evidence is reliable, a trial court should consider (1) whether the scientific principles as to which the witness is testifying are reasonably reliable, and (2) whether the witness is qualified to opine on such matters." Id. (citing Brooks v. People, 975 P.2d 1105, 1114 (Colo.1999)). This reliability inquiry "should be broad in nature and consider the totality of the cireumstances of each specific case," and need not turn on any particular factor or factors. Id. Also, a trial court must issue specific findings as it applies the CRE 702 analysis. Id. at 79.

1 13 Because defendant challenges only the reliability of the scientific principles underly[528]*528ing the Y-STR evidence, we need not address the additional criteria set forth in Shreck and CRE 403.

C. Procedural History

1 14 The court conducted a pretrial Shreck hearing to determine the admissibility of the Y-STR evidence offered by the prosecutor. The court qualified as an expert witness the analyst from the Colorado Bureau of Investigation (CBI) who conducted the Y-STR analysis. She testified about the methodology and reliability of Y-STR analysis generally, and in this case. At the conclusion of the hearing, the court ruled that the Y-STR evidence was admissible under CRE 702 and 403 because: (1) the basic science, methodology, and procedures were substantially similar to the traditional DNA analysis held to be reliable in Shreck,; (2) there was no risk of affirmative misidentification because the Y-STR evidence was used only to show that defendant and his paternal male ancestors could not be excluded as the assailant; (8) the Y-STR evidence was relevant to the identification of the assailant; and (4) the probative value of the Y-STR evidence was not outweighed by the danger of unfair prejudice.

1 15 Later, at trial, the analyst testified to the following:

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Bluebook (online)
2013 COA 161, 318 P.3d 524, 2013 WL 6461467, 2013 Colo. App. LEXIS 1868, Counsel Stack Legal Research, https://law.counselstack.com/opinion/people-v-tunis-coloctapp-2013.