People v. Tunis
| Decision Date | 02 August 2012 |
| Docket Number | Court of Appeals No. 09CA0593 |
| Citation | 2012 COA 126 |
| Parties | The People of the State of Colorado,Plaintiff-Appellee, v. William Anthony Tunis, Defendant-Appellant. |
| Court | Colorado Court of Appeals |
Jefferson County District Court No. 07CR697
JUDGMENT AND SENTENCE AFFIRMED
Opinion by CHIEF JUDGE DAVIDSON
Webb and Plank*, JJ., concur
John W. Suthers, Attorney General, Deborah Isenberg Pratt, Assistant Attorney General, Denver, Colorado, for Plaintiff-Appellee
Leslie A. Goldstein, L.L.C., Steamboat Springs, Colorado, for Defendant-Appellant
*Sitting by assignment of the Chief Justice under provisions of Colo. Const. art. VI, § 5(3), and § 24-51-1105, C.R.S. 2011.
¶1 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 Corrections for an indeterminate term of twelve years to life. His sentence included a determination that he qualified as a sexually violent predator.
¶2 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.
¶3 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) (citingPeople v. Ramirez, 155 P.3d 371, 380 (Colo. 2007)). We disagree with defendant and conclude that the trial court did not abuse its discretion.
¶4 The following was not disputed at trial:
¶5 Every person has a unique genetic code. This code consists of a unique pattern of DNA on the twenty-three pairs of chromosomes 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.
¶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.
¶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.
¶8 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.
¶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.
¶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.
¶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).
¶12 CRE 702 requires that the scientific evidence is both reliable and relevant. See id. at 77. "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. (citingBrooks v. People, 975 P.2d 1105, 1114 (Colo. 1999)). This reliability inquiry "should be broad in nature and consider the totality of the circumstances 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.
¶13 Because defendant challenges only the reliability of the scientific principles underlying the Y-STR evidence, we need not address the additional criteria set forth in Shreck and CRE 403.
¶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 YSTR 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; (3) 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.
¶15 Later, at trial, the analyst testified to the following:
¶16 A DNA sample obtained from the victim's inner thigh shortly after the assault contained male and female DNA. To better analyze only the male DNA, the analyst conducted a Y-STR analysis on this sample. She sought to identify the DNA type at seventeen locations on the Y chromosome and obtained interpretable results at seven of those locations, resulting in a partial profile. At one of the seven locations on the Y chromosome, she observed the presence of DNA from more than one male. She then identified the major male contributor and isolated it for further analysis. The major contributor partial profile matched defendant's profile. After comparing these results to the YFiler Y-STR database and conducting a statistical analysis using the counting method, the analyst testified that she could not exclude defendant and members of his male lineage as sources of the DNA in the inner thigh sample, but she could exclude 99.6% of African Americans, 99% of Caucasians, and 99.5% of Hispanics.
¶17 The Y-STR evidence from the victim's inner thigh is the only YSTR evidence that suggested defendant was the assailant, and is the only Y-STR evidence at issue on appeal.
¶18 We disagree with defendant's arguments that the scientific principles underlying the Y-STR evidence were unreliable.
¶19 The Y-STR evidence was admitted through the testimony of the analyst. Her background included extensive training and experience with the types of partial mixture analyses at issue here, she had been qualified as an expert in forensic DNA analysis in several other cases, she had been conducting Y-STR analysis for approximately one year, and she previously had given expert testimony about Y-STR analysis. See Golob v. People, 180 P.3d 1006, 1012 (Colo. 2008) () (citing Huntoon v. TCI Cablevision of Colo., Inc., 969 P.2d 681, 690 (Colo. 1998)); People v. Lehmkuhl, 117 P.3d 98, 103-4 (Colo. App. 2004) (); see also Shreck, 22 P.3d at 77 (...
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People v. Conyac
...205 P.3d 371, 383 (Colo.App.2007).¶ 22 We review the trial court's admission of expert testimony for an abuse of discretion, People v. Tunis, 2012 COA 126, ¶ 3, 2012 WL 3127296, and will not overturn the court's determination unless it is manifestly arbitrary, unreasonable, or unfair. Peopl......