By Brian Maass

CENTENNIAL, Colo. (CBS4)– The Arapahoe County Sheriff’s Office has made an arrest in an 18-year-old cold case murder following information obtained through a CBS4 Investigation.

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Investigators arrested Robert Lee Williams, 70, on Tuesday. Williams is being held without bond on a murder charge, suspected of killing Arapahoe County prosecutor Rebecca Bartee in June 1999.

Robert Lee Williams (credit: Arapahoe County)

Bartee, 41, was found dead in her bathtub after she failed to show up for work. It appeared someone had staged the scene to make it appear that Bartee had killed herself.

While investigators soon determined Bartee had been murdered, they were never able to make an arrest or charge anyone in the case.

Arapahoe County Sheriff Dave Walcher said of the cold case, “It’s not one I’d hear a lot about. It wasn’t incredibly active.”

Rebecca Bartee (credit: Arapahoe County)

In February of this year, a man contacted CBS4 Investigator Brian Maass, saying he believed he might have crucial information on the Bartee murder. The man said he believed he had cancer and wanted to clear his conscience about what he knew about the Bartee case. He said he had lived with Williams in the Copper Terrace Apartments on South Dayton Street around the time of Bartee’s death.

The witness recalled Williams leaving Bartee’s apartment around the time of the murder and remembered Williams behavior as being strange and suspicious. He said Williams had sexually harassed Bartee. But the man said he had been unable to talk to Arapahoe County investigators. CBS4 connected the witness to Arapahoe County Sheriff investigators who looked into the new information.

“We’re going to act on this and run it into the ground,” said Walcher, referring to the information shared in February by CBS4. “We are going to take it and this is what happens.”

CBS4’s Brian Maass interviews Arapahoe County Sheriff Dave Walcher (credit: CBS)

Walcher said after 18 years, the Bartee family “was shocked and very pleased” at news of the arrest. He spoke to one of Becky Bartee’s sisters Tuesday.

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“When I told her we had an individual in handcuffs and on the way to jail for the murder of Becky Bartee she was stunned. She was incredibly thankful and shocked. If you are the family of Becky Bartee you’re probably thinking, I’m happy someone came forward with some information,” said Walcher.

Rebecca Bartee (credit: Arapahoe County)

Williams was still living at the Copper Terrace Apartments nearly two decades after the murder. His current next door neighbor, Nick Baker, was one of several neighbors who told CBS4 they were stunned.

“He’s the kind of neighbor you wanted to have,” said Baker. “This is kind of shocking.”

The arrest affidavit in the case has been sealed.

But CBS4 has learned that California court records show Williams was arrested in Los Angeles in 1983 and charged with murder. In 1985, he was convicted of voluntary manslaughter in the case and sentenced to four years in prison.

He was released after only two years according to court records. But in 1987, he was again arrested for lewd or lascivious acts with a child under 14. That arrest caused his parole to be revoked and he was returned to prison for about two more years before being released again.

Court records indicate Williams will make his first court appearance on Thursday morning.

Williams declined a request to be interviewed by CBS4.

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CBS4 Investigator Brian Maass has been with the station more than 30 years uncovering waste, fraud and corruption. Follow him on Twitter @Briancbs4.