BOSTON (AP) — Investigators were preparing to seek an arrest warrant for a defrocked Roman Catholic priest long considered a suspect in the 1972 killing of a western Massachusetts altar boy shortly before his death last week, a prosecutor said Monday.

Incriminating admissions Richard Lavigne made in a series of recent interviews while in a medical facility further implicated the longtime suspect in 13-year-old Danny Croteau’s death, Hampden District Attorney Anthony Gulluni told reporters.

Gulluni said his office was prepared to prosecute Lavigne for Croteau’s killing, but he died Friday at the age of 80 before he could be arrested.

Lavigne indicated in interviews this year with investigator that he had brought Croteau to the riverbank, physically assaulted him, left him there and returned sometime later to see the boy floating in the river, Gulluni said.

“I just remember being heartbroken when I saw his body going down the river knowing I was responsible for giving him a good shove,” Lavigne said in one snippet of the interviews played for reporters.

On Friday, before learning about Lavigne’s death, Gulluni had authorized investigators to present the evidence to a magistrate judge in order to obtain an arrest warrant for Lavigne, the prosecutor said.

“Based on the accumulation of evidence, and in particular those admissions, as a prosecutor I believe that I was fulfilling my ethical duties by moving toward the charge of murder against Richard Lavigne … and I believe we could prove it,” Gulluni said.

Lavigne, who always insisted he was innocent, never admitted in those interviews to killing the boy, Gulluni said.

Joe Croteau, Danny’s brother, said his family is disappointed that Lavigne will not be brought to justice, but believe “there’s a higher power and he will face that higher power now.”

Lavigne, the Croteau family’s parish priest was the only named suspect in the killing of the boy found dead in Chicopee, miles from the family’s Springfield home. But a lack of evidence left the case unsolved for decades.

Lavigne had a close relationship with the Croteau’s family and often hosted the boy for overnight visits. Days after Croteau’s body was found, Lavigne asked authorities: “If a stone was used and thrown in the river, would the blood still be on it?”

One of Croteau’s other brothers told authorities a man called shortly after the boy’s death and apologized for what happened to Danny, saying “it was an accident” and that the boy had seen “something” he shouldn’t have. The caller would not identify himself and hung up, but Croteau’s brother said he recognized the voice as Lavigne’s.

Speculation over Lavigne’s involvement intensified after sex abuse allegations against the priest emerged years after Croteau’s death.

The priest pleaded guilty in 1992 to molesting young male parishioners. He was sentenced to 10 years’ probation and seven months of mandatory sex-offender counseling. He was defrocked in 2003.

Croteau was last seen alive on April 14, 1972. His bludgeoned body was found the next day on the banks of the Chicopee River miles from the family’s home in Springfield. An autopsy concluded the boy had been killed with a rock.

Croteau’s family had said they believed the priest abused their son and killed the boy to stop him from reporting it.

Bishop William Byrne of the Springfield diocese said in an emailed statement that Gulluni’s announcement “brings sad closure to a tragic event” that has hung over the community for decades.

“It is incredibly disheartening to learn that a priest, a person ordained to care for God’s people, would have committed such an evil crime and then not taken responsibility for his actions,” he said.

This story has been corrected to reflect that the district attorney’s last name is spelled Gulluni, not Gullini.