A man is Thomas Caldwellin custody after he allegedly voluntarily confessed to killing and raping a young woman in Boston in 1979, according to prosecutors.

Susan Marcia Rose, a 24-year-old with red hair, was killed in an apartment building in Boston's Back Bay neighborhood on Oct. 30, 1979, the Suffolk County District Attorney's Office said Monday.

In August, 68-year-old John Irmer of Oregon walked into the FBI office in Portland and allegedly told agents that he met a woman with red hair at a Boston skating rink around Halloween 1979, prosecutors said.

Irmer said he and the woman walked into 285 Beacon Street, which was under renovation. Irmen then allegedly picked up a hammer and fatally hit her on the head before raping her, according to prosecutors.

Irmer said he left Boston for New York the day after the murder.

A different man was arrested and went on trial for Rose's murder but was acquitted in 1981, prosecutors said.

"This was a brutal, ice-blooded murder made worse by the fact that a person was charged and tried -- and fortunately, found not guilty -- while the real murderer remained silent until now," Suffolk County District Attorney Kevin Hayden said in a statement.

Following the alleged confession, investigators took a DNA sample from Irmer and found that it matched DNA samples from the crime scene, prosecutors said.

Irmer was arraigned on murder charges Monday.