Decades after a single mom was found sexually assaulted and murdered in her Florida home, genetic genealogy has led police to arrest her son’s former football coach for the crime.

When police knocked on his door all these years later, he claimed to have no knowledge of the killing.

But once the handcuffs were on him, the former coach claimed she died after “wild sex” — but police say the evidence points to murder, not a consensual encounter.

A shocking crime

On the morning of Sept. 4, 1981, 31-year-old Linda Patterson Slaten was found strangled to death in her Lakeland apartment, according to Lakeland police.

She was partially nude and had a coat hanger twisted around her neck, according to court documents. Investigators found a window screen had been removed in her bedroom, documents said.

(MORE: Genetic genealogy identifies suspect in teens’ 1982 double murder: Family ‘had lost hope’)

Her two sons, 15-year-old Jeff Slaten and 12-year-old Tim Slaten, had been asleep at the home when she was killed, according to court documents.

“I saw the crime scene. It’s still burned in my brain today,” Tim Slaten said at a Thursday news conference.

Tim told police that his football coach — Joseph Mills — took him home after practice on Sept. 3, according to court documents.

In an interview days later, Mills told police that while dropping Tim off, the boy’s mother came out to the car and thanked him for the ride, documents said. Mills said he left and never returned, documents said.

A novel investigative tool

Sperm was recovered from Slaten’s body, but the DNA did not match anyone in law enforcement databases, according to court documents.

The case then went cold.

“It’s been rough on me my whole life not knowing who it is,” Jeff Slaten said Thursday. “Always being scared to death I was friends with him…. always looking over our shoulder.”

Decades later, in November 2018, investigators looked into using the novel technique of genetic genealogy.

Genetic genealogy compares unknown DNA evidence from a crime scene to public genealogy databases, which are populated by the DNA of family members who voluntarily upload their DNA.

Genetic genealogy has been called a “game-changer” in cracking cold cases. Since the arrest of the suspected “Golden State Killer” in April 2018, about 100 suspects have been identified through the technology, according to Parabon NanoLabs Chief Genetic Genealogist CeCe Moore, who worked on the Slaten case.

In June 2019, after analyzing the DNA in the unknown suspect’s family tree, Parabon analysts told police that Mills was the mostly likely suspect, according to court documents against him.

(MORE: New owner of genealogy website GEDmatch vows to protect users from search warrants)

Mills, now 58, still lives in Lakeland, according to court documents. In the summer of 2019, investigators took Mills’ trash and found that the DNA on it matched the DNA from Slaten’s sexual assault, court documents said.

Authorities also compared Mills’ fingerprints — taken when he was arrested in 1984 — to fingerprints from the victim’s window ledge and found a match, documents said.

‘I trusted this man’

Tim Slaten said Mills kept driving him home from football after his mothers’ murder.

“I trusted this man,” Tim Slaten said Thursday. “He was the last person in my brain I thought was gonna do it.”

“Thank God I didn’t know him,” added Jeff Slaten. “He is a monster.”

An unfounded ‘wild sex’ claim

On Dec. 4, police went to Mills’ home for an interview, during which Mills said he didn’t know anything about the crime, court documents said.

Mills said he didn’t have any relationships with athletes’ parents, including Slaten, and only had small talk when he dropped kids off, documents said. Mills also said he had never been inside the Slaten home.

Mills was arrested for the young mom’s murder on Dec. 12. After he was read his Miranda rights, Mills told police that when he dropped Timothy off that night, Slaten “extended an open invitation to come to her residence for a ‘good time,'” court documents said.

Mills told investigators that in the early hours of Sept. 4, 1981, he returned to Slaten’s home and went inside through an unlocked bedroom window, documents said.

Mills claimed that “Slaten asked him to engage in ‘wild’ sex,” court documents said. “Mills stated upon entering Linda Slate’s bedroom, Linda Slaten already had a wire hanger around her neck as she lay on the bed. Mills stated he twisted the wire hanger around her neck tighter and tighter while engaging in sexual intercourse with Linda Slaten until she lost consciousness.”

Mills told police he then left through the window.

(MORE: Man arrested in intern’s 1980 cold case rape, murder thanks to DNA match)

But police say the crime scene didn’t point to a consensual encounter: there was evidence of a foreign object being used in the rape and Slaten had lacerations consistent with a struggle to get the wire hanger off her neck, court documents said.

Mills is charged with first-degree murder, sexual battery and burglary with assault and battery. His public defender did not immediately respond to ABC News’ request for comment.

Mills made his first court appearance on Dec. 17 and his arraignment is set for Jan. 21.