Police say Theriault, 63, was killed in an altercation with another inmate inside the correctional centre in Dorchester on Feb. 26.
The RCMP did not name the man who will face the charge or what the charge will be.
In February, the RCMP said a 59-year-old inmate at Dorchester had been arrested in connection with ThÃ©riault’s death. The police were calling the cult leader’s death a homicide.
ThÃ©riault led a bizarre cult from 1977 to 1989, first in Ste-Marie de Beauce, Que., then in GaspÃ©, Que., and then Burnt River, Ont., where he lived with eight women, his 26 children and several followers.
He killed his wife and cult member Solange Boislard by disembowelling her, and chopped off the right arm of another commune wife, Gabrielle Lavallee with a chainsaw.
In 1993, ThÃ©riault was sentenced to life in prison and was put in Dorchester, a medium security prison southeast of Moncton that houses about 440 inmates.
In March RenÃ©e Millette, a Montreal lawyer who represents inmates for procedures such as parole hearings, said ThÃ©riault was assaulted often by other inmates over the last two decades.
The Montreal Gazette quoted him as saying, “He was often a victim of his past. The assaults had nothing to do with how he acted while incarcerated. It was because of his past.”
According to Milette Theriault had regrets about his time as the group’s spiritual leader.
Reportedly Theriault told reporters he was plagued by guilt and overwhelmed with shame for the atrocities he committed.
Gabrielle Lavallee, who had her right arm hacked off by Theriault in 1989, wrote a book (French) about her ordeal.
The story of Roch ‘Moses’ Theriault and Lavallee, one of his eight commune “wives,” was also told in Savage Messiah, a 2002 TV movie.