Soil samples taken from under Ruben Flores’ deck contained traces of human blood, a DNA expert testified Monday during the Kristin Smart murder trial.
Thirteen of the tests performed on samples from the Flores property yielded positive results for the presence of human blood, Angela Butler, a senior forensic DNA analyst with the Serological Research Institute in Richmond, said on the stand in Monterey County Superior Court.
The Serological Research Institute tested the soil samples extracted from Flores’ Arroyo Grande property. He is accused of helping his son, Paul Flores, hide Smart’s body, according to court documents.
Another forensic scientist previously testified that those same soil samples had fibers that were red and black — the same colors as the clothing Smart was last seen wearing before she vanished more than 25 years ago.
Paul Flores was the last person seen with Smart before her disappearance following an off-campus party during Memorial Day weekend in 1996. He’s accused to killing the 19-year-old.
Expert ‘can confirm’ human blood in soil samples
Butler previously took the stand on Sept. 12, speaking about her two decades of experience in the forensics field, before court when dark for nearly a week.
On Monday, she testified that there are two tests that are performed when trying to identify human blood.
A presumptive test indicates a chance there may be hemoglobin — a protein found in human blood — and a confirmatory test confirms it, Butler explained. Each test has to be confirmed by a second person before it is reviewed by a third.
Ferret blood or primate blood can also yield a positive test, Butler testified Sept. 12.
However, no ferret or primate remains have ever been found at Ruben Flores’ residence, according to testimony from various witnesses so far.
The confirmatory test is similar to a pregnancy or COVID-19 test, Butler said Monday, with a control line marked “C” and a test line marked “T.” Two lines mean the sample tested is positive for human blood.
“Any activity in the test line is considered a positive result,” Butler said.
So weak positive results, which have a fainter result in the “T” line, are still considered positive.
San Luis Obispo County Sheriff’s Office Det. Clint Cole personally dropped off two soil samples — one labeled “upper soil sample” and the other labeled “deeper soil sample” in March 2021, Butler said.
Tests from the upper soil sample rendered a weak positive presumptive test, but were negative in the confirmatory, she said.
Test results from the deeper soil sample, however, were different.
According to Butler, the sample was split into six parts, with three parts testing positive for the human blood protein, two parts testing weak positive and one negative.
“I can confirm the presence of human blood on all of these samples” except the one, Butler testified.
Her lab received more samples from the Sheriff’s Office the following month, and in total she found 13 positive results, she said.
It was unclear Monday how many tests yielded negative results, or how many tests were performed in total.
‘DNA mixture’ from Paul Flores, Kristin Smart possibly on mattress pad
Some samples Butler received from the Sheriff’s Office had clumps of fibers that she extracted and packaged them for further testing, she said Monday, adding that she gave the fiber samples to Cole.
These are the same fibers Faye Springer, a forensic scientist in Sacramento, testified about earlier in the trial. Some of the fibers were the same color Smart was last seen wearing in 1996 — red shoes and black vinyl shorts.
DNA was not found on the samples that tested positive for human blood, Butler said, adding that degradation, time and conditions could deteriorate DNA presence.
The county also sent Butler’s lab a piece of plywood from a cargo van that belonged to Mike McConville, boyfriend of Paul Flores’ mother, Susan Flores, and a canvas mattress cover presumably from Paul Flores’ 1996 dorm room.
One “very weak” positive result for a presumptive human blood protein test was found on the plywood sample, and because the sample was so small Butler opted to perform a DNA test rather than risk deteriorating the sample more by a confirmatory human blood test, she said.
The DNA test ruled out Smart and both Flores men, but was a match for McConville, Butler said.
Butler said she tested nine areas of the mattress pad for “touch DNA,” or DNA that would be found when someone touches something, such as skin cells or perspiration.
A small brown stain, around the size of a dime, yielded a presumptive positive test for human blood, Butler said.
For the same reason she opted for a DNA test on the plywood sample, Butler said, she decided to test for DNA rather than perform a second blood test.
Results from that DNA test on the mattress pad sample showed a “DNA mixture,” meaning there was more than one person’s DNA found, Butler testified.
She said she used a “probabilistic genotyping” software, which helps analyze DNA, especially degraded and mixed samples.
The software found three possible DNA contributors to the small brown stain, she said, and neither Smart nor Paul Flores cold be included or excluded as a match.
At least one contributor was a male, she said.
The other eight areas did not yield any positive results, Butler said.
Two areas had too many contributors to analyze, she said, and six excluded both Smart and Flores.
Defense cross-examines DNA expert
Paul Flores’ defense attorney, Robert Sanger, focused on how the tests were human blood protein tests were performed, and asked if Butler tested the pH of the samples before testing.
Butler said it isn’t required to test the pH, but that you usually want a neutral pH that is close to water. She did not test the pH, she said.
Sanger asked if she was aware about literature from the test’s manufacturer, Serotec, that said pH lower than 5 could yield false positive results. Butler responded she was aware of the literature, but noted that pH below 5 is “basically battery acid.”
Sanger confirmed test results from the soil samples with her, and pointed out that all of the soil samples tested in 2022 found negative results for human blood.
After lunch, Sanger walked the court through the science behind DNA analysis.
Court adjourned at 2 p.m. Monday — two hours early — to go through exhibits, Monterey County Superior Court Judge Jennifer O’Keefe said.
Butler was expected to continue her testimony Tuesday morning.
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