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DNA evidence lifted from a discarded cigarette led Florida police to the man they believe killed a young mother 35 years ago, authorities said Thursday.

Tonya Ethridge McKinley, then 23, had just left a New Year's Eve celebration before she was strangled and sexually assaulted in Pensacola, allegedly by Daniel Leonard Wells, now 57, according to police.

Daniel Wells was arrested in connection with the 1985 murder of Tonya McKinley in Florida. Escambia County Jail; Pensacola Police

"I didn't really know if this [arrest] would ever happen," the victim's relieved sister, Renee McCall, 62, a nurse, told NBC News on Thursday. "I didn't really think this would happen in my lifetime, not after 35 years."

Detectives said they spoke to dozens of friends and other revelers at Darryl's Bar & Grille, not far from where McKinley was found on Jan. 1, 1985. But for most of the time, they had no suspect in the killing of McKinley, who was survived by an 18-month-old son.

"Despite having a good bit of physical evidence and dozens of interviews, over time, the trail went cold," police said in a statement Thursday. "It seems that every couple of years a new lead would pop up and we would drop everything to run it down. We did this time and time again. 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. "

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But DNA in a public database eventually linked McKinley's killer to Wells' family and then to him, police said.

Investigators were secretly following Wells on March 4 when he tossed a cigarette out of his car, according to an arrest warrant.

Police "immediately stopped and recovered the cigarette butt," which had DNA matching semen taken off the victim's body, according to the warrant.

"Each time, evil won, just out of reach," police said of the 35-year gap. "Until today. Today, the evil that took Tonya from her friends and family was arrested for her brutal murder."

Wells' DNA is being offered to other nearby law enforcement agencies with unsolved sex crimes because he has lived locally the whole time, Pensacola police spokesman Mike Wood said.

"The reasons why this happened, how evil crossed Tonya's path, may never be answered and in the end may not be important," according to police. "What is important is that no one forgot Tonya. "

Wells was booked into the Escambia County Jail on Wednesday and held without bail. He has been charged with murder and sexual battery.

It wasn't immediately clear whether Wells had hired or been assigned an attorney, Wood said Thursday.

McCall said she's pleased about the arrest in her sister's case — but saddened that her dad died a decade ago without knowing that his daughter's alleged killer would someday be caught.

"It weighed a lot on him. She was always his favorite," McCall said of this bittersweet day.