Genetic genealogy test allegedly solved the 35-year-old case.

Authorities in Pensacola, Florida, have arrested a 57-year-old man — with the help of genetic genealogy testing and a cigarette — for the 1985 murder of a young mother.

Tonya McKinley was last seen ringing in 1985 at a restaurant. By the morning, the 23-year-old woman was found strangled and sexually assaulted on the side of the road, police said.

“We collected evidence, interviewed her friends, family, and anyone that may have come across her [that] night,” according to a statement from the Pensacola Police Department. “Despite having a good bit of physical evidence and dozens of interviews, over time, the trail went cold.”

Police said they investigated various leads over the last 35 years as “the next generation” of detectives picked up the case.

“In the meantime, a baby boy grew up without a mother, parents buried their daughter without knowing justice, and a killer was walking around free,” according to police.

Mike Wood, public information officer with the Pensacola Police Department, said officers “worked for over a year using genealogy” to try to find a link to the suspect.

In the end, DNA recovered from the alleged killer’s cigarette butt and genetic genealogy testing helped solved the cold case.

Police zeroed in on a man named Daniel Wells after a member of his family appeared in their database search. Officers surveilled Wells and took one of his discarded cigarette butts. Wells’ DNA matched the DNA at the crime scene.

“They basically made a family tree, started eliminating people and got to Daniel,” Wood said.

Police Chief Charles Mallett posted to social media a heartbreaking phone call to McKinley’s son as he learned that his mother’s alleged killer was arrested.

Wells, 57, was arrested on Wednesday and is held without bail in Escambia County Jail on murder and sexual battery charges. An attorney for Wells was not listed on the jail’s website.

“You may now rest in peace Tonya Ethridge McKinley,” the police said.