Kristin Smart trial: DNA expert testifies on human blood
Soil samples taken from under the Ruben Flores Bridge contained traces of human blood, a DNA expert said Monday at Kristin Smart’s murder trial.
Thirteen of the tests performed on samples from the Flores property returned positive results for the presence of human blood, said Angela Butler, senior forensic analyst at the Richmond Serological Research Institute, at the Superior Court stand. of Monterey County.
The Serological Research Institute tested the soil samples extracted from the Arroyo Grande de Flores property. He is accused of helping his son, Paul Flores, hide Smart’s body, according to court documents.
Another medical examiner previously testified that those same soil samples contained red and black fibers – the same colors as the clothes Smart last saw before disappearing more than 25 years ago.
Paul Flores was the last person seen with Smart before he disappeared following an off-campus party over Memorial Day weekend in 1996. He is accused of killing the 19-year-old.
Expert ‘can confirm’ human blood in soil samples
Butler previously spoke on Sept. 12, speaking about his two decades of experience in the field of forensics, in court when it was dark for nearly a week.
On Monday, she testified that there are two tests that are done when trying to identify human blood.
A presumptive test indicates a chance there is hemoglobin — a protein found in human blood — and a confirmatory test confirms it, Butler explained. Each test must be confirmed by a second person before being reviewed by a third.
Ferret or primate blood can also test positive, Butler said Sept. 12.
However, no ferret or primate remains have ever been found at Ruben Flores’ residence, according to the testimonies of various witnesses so far.
The confirmatory test is similar to a pregnancy test or the 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.
Thus, weak positive results, which have a lower result in the “T” row, are still considered positive.
Det. from the San Luis Obispo County Sheriff’s Office. Clint Cole personally deposited two soil samples — one labeled “upper soil sample” and the other labeled “deeper soil sample” in March 2021, Butler said.
Tests of the upper soil sample returned a weakly positive presumptive test, but was negative in confirmation, she said.
The 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 weakly positive and one negative.
“I can confirm the presence of human blood on all of these samples” except for this 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 not known as of Monday how many tests had returned negative results, or how many tests had been carried out in total.
‘DNA Mix’ by Paul Flores, Kristin Smart possibly on a mattress topper
Some samples Butler received from the sheriff’s office contained clumps of fibers that she extracted and packaged for further testing, she said Monday, adding that she gave the fiber samples to Cole.
These are the same fibers that Faye Springer, a forensic scientist in Sacramento, testified to earlier in the trial. Some of the fibers were the same color Smart was last seen in 1996 – red shoes and black vinyl shorts.
DNA was not found on samples that tested positive for human blood, Butler said, adding that degradation, time and conditions could deteriorate the presence of DNA.
County also sent Butler’s lab a piece of plywood from a van that belonged to Mike McConville, boyfriend of Paul Flores’ mother, Susan Flores, and a canvas mattress cover presumably from Paul Flores’ dormitory in 1996.
A ‘very weak’ positive result for a suspected 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 it. further sample by a confirmatory human blood test, she said.
The DNA test ruled out Smart and the two Flores men, but was a match for McConville, Butler said.
Butler said she tested nine areas of the mattress pad for “touching DNA,” or DNA that would be found when someone touches something, such as skin cells or sweat.
A small brown speck, the size of a penny, gave 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 DNA rather than take a second blood test.
The results of that DNA test on the mattress cover sample showed “mixed DNA,” meaning there was more than one person’s DNA found, Butler said.
She says she used a “probabilistic genotyping software”, which helps to analyze DNA, especially degraded and mixed samples.
The software found three possible DNA contributors to the little brown spot, she said, and neither Smart nor Paul Flores can be included or excluded as a match.
At least one contributor was a man, 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 questions DNA expert
Paul Flores’ defense attorney, Robert Sanger, focused on how the tests were done, and asked if Butler tested the samples for pH before the test.
Butler said there’s no need to test for pH, but generally you want a neutral pH close to water. She didn’t test the pH, she said.
Sanger asked if she was aware of literature from the test manufacturer, Serotec, that a pH below 5 could give false positive results. Butler replied that she was aware of the literature, but noted that a pH below 5 is “essentially battery acid”.
Sanger confirmed with her the soil sample test results and pointed out that all soil samples tested in 2022 had found negative results for human blood.
After lunch, Sanger presented the science behind DNA analysis to the court.
The court adjourned at 2 p.m. Monday — two hours earlier — to consider exhibits, Monterey County Superior Court Judge Jennifer O’Keefe said.
Butler was scheduled to continue his testimony Tuesday morning.
This story was originally published September 19, 2022 1:27 p.m.