DAVENPORT, Iowa (KWWL) -- It felt like a science class in the courtroom Friday for the murder trial of Jerry Burns.
Burns is accused of killing Michelle Martinko in 1979. The case had gone cold until Burns' arrest in December 2018.
Retired investigators and criminalists, who took the stand, recalled how they collected the thing that would eventually lead to Burns' arrest, DNA.
Michael Peterson, retired from the Iowa Department of Criminal Investigation, said a "mixture of DNA" was found on Martinko's clothes.
In 2018, authorities used genealogical research to narrow down the suspect pool, eventually they landed on Burns.
"That if you have a result that can only be found in 1 in one billion people, and we only have 3 or 4 billion people on earth, then probability that two unrelated individuals would have that profile, can be discounted," said Linda Sawer, who worked with Peterson at the criminalistics lab. In 1979, there were only about 3 or 4 billion people on the planet.
The defense questioned if the evidence could have been contaminated over the last 4 decades.
"I don't want to sound like I'm cavalier about the idea of contamination. Certainly contamination is something that is always considered as a possibility. I would say that, for my examination of this particular item, I have no indications of there being a contamination issue," Peterson said.
Much of the day was also spent following the chain of evidence in the case with each witness going over when and how they encountered the evidence.
The trial adjourned for the weekend. It's set to resume on Monday at 9 a.m.