A man who was convicted of throwing a student nurse to her death from a hospital roof in 1958 later walked away from a prison work farm and lived under an alias for decades, even marrying and earning a college degree, before he died in 2004, authorities said Thursday.

A six-month investigation by a cold case unit of the U.S. Marshals Service found that Shirley Campbell died of a heart attack in New Mexico at age 67 after living for more than three decades as Edward Davis. Using that identity, Campbell married a woman who had no clue about his past, earned a bachelor's degree in sociology and was hired by New Mexico as an employment counselor.

Campbell was convicted of killing 19-year-old Sylvesta Andy, who was a student nurse and a patient at a hospital in Hamilton, Ohio, where Campbell worked as an orderly. Campbell was accused of sexually assaulting Andy in a hospital elevator, chasing her to the roof and then pushing her to her death five stories below.

Campbell was on parole at the time on charges related to a robbery and attempted sexual assault of a taxi driver. He was 20 when he confessed to killing Andy and was sentenced to life in prison. He escaped from a prison work farm in Chillicothe, Ohio, in 1972.

The Marshals Service cold case unit in northern Ohio, which includes investigators from the Ohio Adult Parole Authority, began looking for Campbell in April. Deputy Marshal David Siler said Thursday that deputy marshals on the West Coast learned that Campbell assumed his new identity in the Los Angeles area after his escape from prison.

It was there that Campbell built a new persona. He told people that he was adopted, that his wife and two daughters had died in a fire and that he'd served with the U.S. Army in Vietnam, none of which was true. It's also believed that Campbell got help from relatives after his escape.

Siler said someone has to be a "great actor" to successfully remake a life under a new identity.

"The prison identified him as someone who can assimilate to any situation," Siler said.

Campbell's wife was in "total disbelief" when she learned about his past, Siler said.

Investigators tracked Campbell from Los Angeles to New Mexico, where he moved in the mid-1980s. After attempting to identify every Edward Davis who lived in the state, marshals narrowed the list to about a half-dozen before they found Campbell and learned about his death.

It's the fourth decades-old prison escape that the cold case unit has solved since it formed in April.

"We will continue to follow each and every lead to uncover the trails of these fugitives and bring closure to the victims' families," said Pete Elliott, the U.S. Marshal for northern Ohio.