During her opening statement last week, the prosecutor trying the homicide case against John Minch told the jury, "The science doesn't lie. It's his hair."
But maybe not.
The prosecution's own DNA witness testified Tuesday that the type of hair fragment found in Melissa Groot's hand the day she was slain on May 6, 1999, in her Bethel Park home, could be expected in about 1 percent of the caucasian population of North America.
"It could have come from John Minch," said Terry Melton, the lab director at Mitotyping Technologies in State College.
Throughout her testimony in the fourth day of trial, Ms. Melton used qualifiers like "could." She repeated to the jury that unlike nuclear DNA, "mitochondrial DNA is not a unique identifier."
"So there's no way, through mitochondrial testing, [to tell] that any one sample comes from any one person?" asked Mr. Minch, who is representing himself.
"That's correct," Ms. Melton answered.
Investigators on the Groot case found several hairs on the woman's nightgown immediately after her death in 1999.
However, they weren't tested by a laboratory for more than eight years.
Assistant district attorney Lisa Pellegrini asked Pam Woods, who works for the Allegheny County medical examiner's office, about the delay.
Ms. Woods never clearly answered the question and simply said she wasn't in the section that did hair analysis at the time of the stabbing.
Later, another lab examiner said that the hair was in storage with the Allegheny County police from 2004 to 2007 because the ME's lab ran out of room.
After examining all of the hairs found on Groot's nightgown, Ms. Melton said that eight of them belonged to Groot's husband at the time, David Groot.
But four additional hairs were found on it that have not been matched to anyone -- including samples that were collected from all of the first responders at the scene that day.
Only the single, 2.5 cm hair fragment could be tied to Mr. Minch.
During his cross-examination, Mr. Minch gave Ms. Melton a hypothetical. If a county has 1 million white people in it, he said, and 1 percent of that population has the same hair type, "Would that not come out to 10,000 people in that county alone?"
"Yes," she answered. But then she added, "However, that also tells me that 99 percent of them could not have left that hair."
She said the statistics generated by mitochondrial testing are "a way to generalize."
During her testimony, Ms. Melton also told the jury that the hair fragment that matched Mr. Minch was consumed by the testing process and could not be retested or re-examined.
"It's better to consume the hair and get a result than take half the hair and get nothing," she said.
During cross-examination, Mr. Minch spent much time with Ms. Woods trying to elicit information about a white fiber that was reported to have been intertwined around the hair fragment that matched him, but was never examined.
"Did you make any attempt to find out where this fiber came from?" he asked.
"I did not," Ms. Woods answered.
She said she believed it was a shed hair that had been stuck on clothing and dropped.
"But that is just an assumption," Ms. Woods said. "It's an opinion."
In reports, one lab examiner described the fragment as "very light brown," and another described it as "medium to dark brown."
Mr. Minch questioned the inconsistency in the descriptions and then asked if it was possible the hair fragment was embedded in the nightgown for a long period of time, or in the headrest of a car.
And in either case, he continued, could multiple launderings change it or could exposure to the sun change it?
"Yes, it is possible," Ms. Woods said.
Also Tuesday, Mr. Groot concluded his testimony that began Friday.
On cross-examination by Mr. Minch, he said he met Melissa Groot online, and that they began seeing each other while she was still married to Mr. Minch.
The defendant also asked Mr. Groot about whether he asked a co-worker the day after his wife's death to provide an alibi for him to police.
"I would not have asked him to lie," Mr. Groot answered.
Asked if he was seen laughing and joking at the crime scene that day, Mr. Groot said he didn't recall that, but that if he was he was attempting to comfort his wife's mother.
Ms. Pellegrini wrapped up her examination of Mr. Groot by asking, "Did you kill Melissa?"
"No," Mr. Groot answered.
"Did you love her?"
"Yes, I did," he continued.
"Did you have anything to do with her murder?" Ms. Pellegrini concluded.
Paula Reed Ward: email@example.com, 412-263-2620 or on Twitter @PaulaReedWard.