The science of DNA profiling was part of the testimony last week in the Sophie Sergie cold-case murder trial. Criminologists testified about how body fluids found on the victim lead to the unknown DNA profile thought to be the victim’s rapist.
Forensic scientist Kristin Denning told the jury that she has found semen in the bodies of living sexual assault victims up to a week after an attack. Sometimes even if seminal fluid has drained out of the woman’s body.
“It’s a gradual loss due to gravity, which would mean the individual is upright, and moving around.”
But there was no semen found in the victim’s underpants, which suggests she did not get up again.
Denning testified in her role as an Alaska criminal scientist who examined microscope slides of fluids and semen found in the 1993 murder of 20-year-old Sophie Sergie in a college dormitory bathroom. When questioned about the semen showing if Sergie was sexually assaulted, Denning said she could not say.
Defense attorney James Howaniec asked Denning if Sergie had sex the Saturday that she arrived in Fairbanks, or sometime on Sunday, would semen from that encounter be present after her death Monday morning?
“It’s very difficult to determine time since intercourse,” she said.
DNA specialist Dr. Abirami Chidambaram also worked in the Alaska Scientific Crime Detection Laboratory. She testified about her report from May 17, 2000, when techniques for profiling had much improved since the 1993 murder.
“The DNA profile can be compared to the blueprint. It gives a snapshot, in a sense, of how to identify a person at the molecular level,” she said.
She explained how she made a reference DNA profile for Sophie Sergie, so she could compare it to any others. Then she compared that known DNA to the unknown profile extracted from semen found in the victim’s vagina. She explained to prosecutor Chris Darnall how the profiles were different.
Chibambaram: “I extracted DNA from the dried blood sample, from Miss Sergie, took both the samples through amplification and then data analysis.”
Darnall: “Okay. So were these the same profile or were they different?”
Chibambaram: “Oh, they were definitely different. To start with, Sophie Sergie's sample came out of a female and the other extraction obviously had an X/Y which meant it was a male.”
Darnall: “What were you able to determine about that sample? The one taken from the vaginal swab?”
Chibambaram: “Obviously it came from a male. It was a very robust sample in terms of quality and quantity. “
Darnall: “Okay. How many sources contributed to this sample?”
Chibambaram: “Just one. There was absolutely no question about that.”
Chibambaran testified that it became common practice, when an unknown profile was found as part of a crime, to send it to the FBI.
“Any unknown profile from casework gets entered into the FBI's CODIS system. CODIS stands for Combined DNA Index System. It is a warehouse almost, of human genetic profiles. It contains genetic profiles for missing persons and unidentified human remains, military personnel, convicted offender samples.” She explained.”
“You hope that you put it in this massive database that maybe there is another similar profile there that's going to match.”
There never was a match from that database, but in 2018, the profile developed from the semen found in the victim partially matched the profile of a woman who submitted her DNA to a genealogy website. That woman was Steven Downs’ aunt. Downs was living in the same dormitory at the time of the killing and became a prime suspect. He was arrested in 2019.
The courtroom is closed to the public to prevent COVID-19 sickness. But the court is video streaming the trial on the Alaska Court System website. Prior permission to record the proceeding for this story was granted.
