People.com Crime Iowa Teen Was Fatally Stabbed in Mall Parking Lot Decades Ago — and Her Killer Was Just Convicted Jerry Burns faces a mandatory life sentence after being found guilty of fatally stabbing 18-year-old high school senior Michelle Martinko By KC Baker Published on February 25, 2020 12:34 PM Share Tweet Pin Email Photo: Cedar Rapids Police Department On Dec. 19, 1979, outgoing, popular Iowa teen Michelle Martinko went to the local mall to look for a new coat. She never returned home. At 4 a.m. the next morning, police made a chilling discovery when they found the 18-year-old’s bloodied body crumpled in the passenger well of her family’s Buick Electra in the mall’s parking lot. The high school senior been stabbed numerous times in the face and chest. For decades, her case remained cold. Still, investigators worked tirelessly to find her killer. On Monday, thanks to advances in DNA technology, Martinko’s killer, Jerry Burns, 66, was brought to justice when a jury found him guilty of first-degree murder, the Des Moines Register reports. He faces a mandatory life sentence. He can appeal the verdict, which jurors reached in just 3 hours. “We don’t exactly know the whys and some of the details, but we definitely know who did it and that was terribly important to us,” Janelle Stonebraker, Martinko’s older sister, said after the verdict, the Des Moines Register reports. /AP/Shutterstock During the trial, prosecutors said Burns stabbed Martinko inside her family’s car outside the mall, The Gazette reports. Want to keep up with the latest crime coverage? Sign up forPEOPLE’s free True Crime newsletter for breaking crime news, ongoing trial coverage and details of intriguing unsolved cases. Found fully clothed, Martinko was not sexually assaulted, but the knife the killer wielded pierced her lungs and aorta, the Associated Press and Time report. Authorities still do not know why Burns targeted or killed Martinko. No fingerprints were left at the scene. But DNA — in the form of blood found on the car’s gearshift and Martinko’s dress — was, the Des Moines Register reports. Over the years, as technologies advanced, investigators were able to use the DNA found at the scene and DNA that had been entered in GEDmatch, a public genealogical database, to construct DNA profiles of three possible suspects, who were three brothers in Iowa, the Des Moines Register reports. Using a straw that Burns threw out at a pizza restaurant, investigators were able to connect him to Martinko’s murder. On Dec. 19, 2018, the 39th anniversary of Martinko’s slaying, police arrested Burns at his business in Manchester, local station KCRG reports. He pleaded not guilty to the charge. Calling Martinko’s murder “a case that has haunted our community for decades,” Cedar Rapids Police Chief Wayne Jerman said in a statement, “For Michelle’s family and friends, we know that the pain of losing a daughter, sister, or friend will never go away. “You and Michelle will forever be in our thoughts and we are eternally grateful for your support, trust, and confidence over the many years.” Burns’ attorney Leon Spies did not immediately return PEOPLE’s calls for comment.