NEWS

Evidence dispute prompts ‘DNA master class’

Andrea Fisher
anfisher@greatfallstribune.com

The defense in the Tommy Dellar rape trial called the case a classic example of “he said, she said.” However, there is some physical evidence involved, specifically DNA.

Before the trial began, presiding District Judge John Kutzman ruled on an objection from the defense regarding sperm cells attributed to the defendant that were collected from a stain in the woman’s underwear.

The defense made it clear it does not trust the science behind the DNA analysis process conducted at the Montana State Crime Lab, based on statements made by attorney Mark Frisbie at a pretrial motions hearing earlier this month.

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Forensic scientist Jennifer Revis-Siegfried conducted the testing at the crime lab. She testified at the hearing and is expected to be called as the first trial witness.

Revis-Siegfried provided extensive testimony about the DNA testing process, including how sperm cells are isolated from epithelial cells, or skin cells, for further testing.

In this case, a swab of the stain was taken from the woman’s underwear, the cells present in that stain were mixed with a solution and spun at a high rate of speed to allow the heavier sperm cells to be separated from the epithelial cells.

Revis-Siegfried explained that although this process is the standard within the scientific community, extractions are most commonly not “perfect,” as some of the epithelial cells remain with the sperm cells. For this reason, the scientific community refers to the portion including sperm cells as the “sperm cell fraction.”

The test results in this case show Dellar’s DNA was found in the largest amount in the sperm cell fraction. The woman’s DNA could not be excluded from the sample, however, Revis-Siegfried said the lab typically finds cells belonging to the person who wore the undergarments in stains of this kind.

“How do we know it’s good enough?” Frisbie asked of the testing process.

Revis-Siegfried noted the proses is used by crime labs across the country, and those labs are audited by the FBI. She testified Montana’s lab passed the last audit.

Court records show there was no legal basis to exclude the test results, as the science is sound. The defense was able to challenge the use of the term “sperm cell fraction,” and the general description of the underwear stain as a “semen stain.”

Kutzman granted this request, though he explained the witness could still use the words “sperm” and “semen” when explaining the testing process and results to the jury.

Revis-Siegfried instead called the sample the “mostly non-epithelial” portion during her testimony Tuesday afternoon as the state’s final witness. She explained to the jury that such a sample contains sperm cells and carry-over epithelial cells.

She also explained the test results to the jury, noting that Dellar contributed the most DNA to the sample from the stain.