MONTREAL -- The Roman Catholic Archdiocese of Montreal has ordered an "independent, external" investigation into the case of Brian Boucher, a Montreal priest who sexually assaulted two boys.

In March, Boucher was sentenced to eight years in prison for sexually assaulting the two minors, now adults. Boucher worked in 10 Montreal-area churches between 1985 and 2015. The abuse took place at two churches, between 1995 and 1999 in the case of one victim and between 2008 and 2011 in the other. The case was unusual because it was the church that investigated it, and turned Boucher over to police.

After Boucher's sentencing, the church named retired judge Anne-Marie Trahan to investigate how and why church abuse remained undetected for 70 years, but Trahan died this summer. The investigation will now be conducted by Pepita Capriolo, a retired Quebec Superior Court justice, the Archdiocese announced Monday. Capriolo's investigation will focus specifically on Boucher and how he avoided detection for so long.

"We want to get to the bottom of things to uncover the truth regarding how the concerns and complaints about Brian Boucher were received and handled, " Montreal Archbishop Christian Lépine said. "Ms. Capriolo's mandate is twofold: first, determining 'who' knew 'what' and 'when,' and then making recommendations to ensure that our policies and procedures improve, thereby avoiding that such crimes would occur again."

Lepine said the Archiodocese would provide Capriolo with "all the resources needed to conduct a thorough investigation" and will make the results of her completed investigation public.

"The Roman Catholic Archdiocese of Montreal has taken on the important task of shedding light on the factors that may have allowed Brian Boucher's behaviour to go undetected," Capriolo said. "I am pleased to be invited to undertake this important work and grateful for the commitment of full independence and the support that has been assured to me."

Capriolo will need to determine a timeline of who knew what and come up with recommendations to improve procedures.

A group of victims have filed a class-action lawsuit against the Catholic Church.  

The Canadian Press contributed to this report.

With files from CTV Montreal's Stephane Giroux