MINNEAPOLIS (AP) — Billy Glaze, the drifter convicted of murdering three American Indian women in Minneapolis in the 1980s, died Tuesday in prison, said an attorney who was hoping to use new DNA testing to exonerate Glaze.

Glaze died at a Delaware prison after being diagnosed with stage-four lung cancer late last week, said Ed Magarian, one of his attorneys. The Delaware Department of Corrections said an elderly inmate serving a life sentence after being convicted in Minnesota died Tuesday in the infirmary at the James T. Vaughn Correctional Center of natural causes following a terminal illness. The Corrections Department did not identify the inmate, but Magarian confirmed to The Associated Press that Glaze died at that prison.

Lawyers for the Minnesota Innocence Project had been arguing in court that new DNA testing of evidence from the murder scenes found no link to Glaze.

But prosecutors were confident they had the right man and said Glaze did not need a new trial. Hennepin County Attorney Mike Freeman had said the Innocence Project’s evidence is “inconclusive and unpersuasive” and doesn’t meet legal standards for a new trial.

“Billy spent almost 30 years in prison for a crime he didn’t commit. That tragedy has been compounded by his death. We’re heartbroken, particularly as we were confident that Billy would have been exonerated in 2016, and released from prison as a free man,” Magarian said in a statement. He said Glaze’s lawyers are researching Minnesota law to see if there’s a way to clear his name after his death.

In 2014, lawyers from the Minnesota Innocence Project, the Innocence Project in New York and Magarian’s law firm, Dorsey & Whitney, filed papers to vacate Glaze’s conviction and to win him a new trial based partly on the new DNA evidence.

Glaze was serving three life sentences for the murders of 19-year-old Kathleen Bullman, 26-year-old Angeline Whitebird Sweet and 21-year-old Angela Green, in 1986 and 1987. The bodies of the women were found in three locations frequented by transients in Minneapolis. All three were found nude or mostly unclothed with their bodies positioned in ways that suggested a serial killer.

Glaze had spent more than 25 years behind bars. His conviction in 1989 was based largely on testimony from witnesses and jail inmates.

Prosecutors also presented a note that Glaze had purportedly written in jail saying, “I killed them. I was mad at them.”

Innocence Project attorneys contended the witness testimony was unreliable and the physical evidence, including the note, didn’t prove him guilty.