Image copyright Pensacola Police Image caption Police took DNA evidence from a cigarette butt that Daniel Wells threw out of his car

DNA evidence from a discarded cigarette has led Florida police to arrest a man on suspicion of murdering a woman 35 years ago.

Daniel Wells, 57, was arrested and charged in Pensacola earlier this week for the murder of Tonya McKinley.

Ms McKinley was found strangled and sexually assaulted on New Year’s Day in 1985, leaving behind a baby son.

Her case has gone unsolved, but police say DNA from a public database linked Mr Wells to her murder in Pensacola.

"I didn't really know if this [arrest] would ever happen," Ms McKinley’s sister, Renee, told NBC News. "I didn't really think this would happen in my lifetime, not after 35 years."

In a statement, Pensacola police said they interviewed her friends and family. Police also spoke with other people who were celebrating New Year's Eve at a local restaurant where the 23-year-old was last seen.

But until this week, no suspect has been named.

"Despite having a good bit of physical evidence and dozens of interviews, over time, the trail went cold," police said. "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".

How did police trace the suspect?

Their success came after comparing open-source genealogy databases with DNA evidence found near McKinley’s body. Detectives in California used the same method to find Joseph James DeAngelo, a suspect in the infamous Golden State Killer cases.

The database led Pensacola police to several different people believed to be Mr Wells’ distant cousins. After the discovery, authorities built a family tree to identify suspects, and subsequent investigations led to Mr Wells.

Police tailed him and took DNA evidence from a cigarette butt that he threw out of his car.

Mr Wells has been charged with first-degree murder and first-degree sexual battery, and is being held at Escambia Country Jail.

Timothy Davidson Jr, Ms McKinley’s 35-year-old son, told The Daily Beast that he was happy at the news of the arrest, but would only feel “complete when there is a conviction and justice has been served.

“It’s still kind of unbelievable, like I’m dreaming,” he added.