Convicted Canadian serial killer Robert Pickton, who killed over 20 women, has been hospitalized and is in life-threatening condition after an assault at a Quebec prison, authorities said Tuesday.

The 74-year-old was convicted of six counts of second-degree murder and sentenced to life in prison in 2007, with the maximum parole ineligibility period of 25 years, after being charged with the murders of 26 women.

The remains or DNA of 33 women, many picked up from Vancouver’s Downtown Eastside, were found on Pickton’s pig farm in Port Coquitlam, British Columbia. Prosecutors previously said Pickton told an undercover officer planted in his jail cell that he killed 49 women and intended to make it “an even 50.”

Vancouver police were criticized for not taking the cases seriously because many of the missing were sex workers or drug users.

The Correctional Service Canada first announced on Monday that an inmate had been sent to hospital after a serious assault at the maximum security Port-Cartier Institution, about 300 miles northeast of Quebec City.

On Tuesday, the correctional service confirmed Pickton was the inmate injured in a major assault Sunday and that none of its staff were involved in the attack.

Quebec provincial police said the sentenced killer’s injuries were considered life-threatening.

Police spokesman Hugues Beaulieu said a 51-year-old suspect was in custody for the assault.

Pickton’s confirmed victims were six: Sereena Abotsway, Mona Wilson, Andrea Joesbury, Brenda Ann Wolfe, Georgina Papin and Marnie Frey.

At the time of Pickton’s sentencing, British Columbia Supreme Court Justice James Williams said it was a “rare case that properly warrants the maximum period of parole ineligibility available to the court.”

Last month, 12 mayors from the Vancouver area sent a letter to the federal justice minister demanding that Pickton never be granted day parole, the Vancouver Sun reported. Pickton is eligible for day parole and will be eligible for full parole in 2027, the newspaper reported.

Police began searching the Pickton farm in the Vancouver suburb of Port Coquitlam more than 22 years ago in what would be a years-long investigation into the disappearances of dozens of women.

During his trial, videotaped interviews were played in which Pickton denied knowing the victims and asked a police officer: “Do I look like a murderer?”

In 2016, a book reportedly written by Pickton was removed from Amazon’s website a day after being put on sale online following protests by Canadian authorities.