Geoghan was killed in his jail cell by Joseph Druce, 37, a convicted murderer said to bear a grudge against homosexuals.
Quoting a union representative for prison guards, The Washington Post reported that Druce had followed Geoghan into his cell after lunch. He bound and gagged Geoghan before strangling him with a bedsheet.
Druce jammed the electronically operated cell door to prevent guards from opening it, tied Geoghan's hands behind his back and gagged him, The Post said.
He then repeatedly jumped from the bed in the cell onto Geoghan's motionless body, according to the account by Robert Brouillette, an executive of the Massachusetts Correction Officers Federated Union.
Worcester County District Attorney, John Conte, has declined to comment on how Geoghan was choked, saying that an autopsy is planned for Monday – when murder charges will be filed.
"I can't understand why they would put a guy who would kill a sex offender in a cell with a sex offender."
Joseph Druce's father
Geoghan was held in protective custody in a special section of the Souza Baranowski prison, 100 km northwest of Boston. He had limited contact with other prisoners.
But officials refused to say how Druce, whose father said he held a grudge against homosexuals, managed to get near Geoghan.
"We can't release any details because the District Attorney's office is conducting an investigation," said Kelly Nantel, a spokeswoman for the Department of Corrections. Druce, who is serving a life sentence for murdering an elderly man, is now in isolation at the facility.
Psychiatrists say child molesters are often at great risk in prison because their fellow inmates – convicted rapists, murderers and robbers – tend to classify them as the most heinous criminals of all.
The Boston Globe reported that Druce's father, Dana Smiledge, said, "I can't understand why they would put a guy who would kill a sex offender in a cell with a sex offender."
Geoghan was a central figure in the sex scandal that rocked through the Roman Catholic Church in the US and abroad.
"I had a moment of thinking 'He got what he deserved' "
one of the victims
The 68-year-old child rapist was serving a sentence for groping a boy while they were swimming, and was awaiting trial for charges that dated as far back as the 1960s.
His prosecution helped uncover a string of paedophile cases that forced Cardinal Bernard Law to resign last year as leader of the Boston Archdiocese, home to more than 2 million Catholics in the United States.
Many of the 130 people who have filed lawsuits against Geoghan expressed shock at his death.
"I had a moment of thinking 'He got what he deserved'," said Michael Linscott, 45, when he heard the man who had molested him as an altar boy 37 years ago was murdered.
"As victims we will live in our own prison forever, but Geoghan got off easy. He is never going to hurt anyone again, but he still had a lot of penance to do on earth," Linscott said, biting his lip at a news conference.
His death has come at a time where the Church is offering to pay $65 million to settle abuse cases. It is unknown how the killing will affect the talks, lawyers said.