DNA expert testifies at length about DNA in Aguirre case; defense expert set to respond Tuesday

A DNA expert for prosecutors testified Monday that a small amount of DNA likely from Ruby Doss was detected on the condom found near her body mixed with DNA from Richard Aguirre, the man accused of killing her.

Former Washington State Patrol crime lab employee Lorraine Heath testified at length Monday about a new software program that allowed her to detect Doss’ DNA when other forms of analysis had not, a point that the defense called into question.

It’s the fourth week of testimony in 59-year-old Aguirre’s bench trial for the 1986 killing of Doss.

Doss, 27, was found beaten and strangled near East Sprague Avenue on a cold January night.

A condom was found not far from Doss’ body and was destroyed in testing in 1989 by a LifeCodes forensic scientist. DNA testing was in the early stages in the late 1980s.

Extracts from the condom were then separated into a sperm and nonsperm fraction. Doss’ DNA was never detected in the nonsperm fraction, after testing at multiple private labs over decades.

Heath swabbed the inside of the original envelope in 2017 and tested for any residual DNA from when the condom was placed inside.

She found a mixed DNA profile, the male portion of which matched Aguirre. At the time, a new type of analysis called probabilistic genotyping was being used at private labs and being validated by the WSP Crime Lab.

Probabilistic genotyping is a software that allows for better mathematical examination of existing data, Heath said.

She sent the data to CyberGenetics, a company that uses its TrueAllele software to perform probabilistic genotyping.

TrueAllele excluded Doss as a contributor to the nonsperm portion of the sample taken from the condom envelope; however, Heath testified she had concerns about CyberGenetics’ report, because they did not use a threshold to tune out background noise on their electropherogram, a chart of the DNA fragment sizes.

Heath said government labs must validate new technologies themselves and within their specific system determine the threshold to accurately tune out background noise.

So Heath reran the probabilistic genotyping on STRMix, the software WSP had validated for use in the state crime labs.

With a threshold, she found that it’s 8,100 times more likely that the DNA from the original condom package is a mixture of Aguirre’s and Doss’ DNA than a mixture of Aguirre’s and a random woman’s DNA.

Aguirre’s attorney, Karen Lindholdt, questioned Heath extensively about probabilistic genotyping, reading emails between Heath and CyberGenetics that showed a disagreement on the importance of the threshold in conducting the analysis.

Heath and prosecutors did not obtain CyberGenetics’ full report prior to Aguirre’s first trial, which ended in a hung jury.

Lindholdt asked whether Regina Palmer, the receptionist at LifeCodes who opened the condom package to verify there was a condom inside, had been excluded as a contributor.

Heath said she did not have a sample for comparison to determine one way or another.

Following Heath’s testimony, the prosecution rested its case. Lindholdt then motioned to dismiss the charges, citing a lack of evidence.

Spokane County Superior Court Judge Jeremy Schmidt denied her motion following an analysis of the evidence, which on this type of motion must be viewed in a light favorable to the state.

Lindholt plans to call her DNA expert Tuesday morning. Aguirre’s trial is scheduled to end this week.