The Correctional Service of Canada (CSC) says it will be doing an "additional review" on the security classification of one of Canada's most notorious serial killers after they were transferred to a medium-security prison.

This article includes descriptions of violence and sexual assault.

The move of Paul Bernardo by the CSC from a maximum-security prison in Ontario to a medium-security prison in Quebec, first reported on by Kingstonist, sparked outrage from many Canadians.

Canada’s minister of public safety, Marco Mendicino, even described the decision as “shocking and incomprehensible” on a social media post.

Bernardo, 58, has spent a decade at Millhaven Institute, a maximum-security facility with a capacity for almost 500 inmates. Now, he's continuing to serve a life sentence at La Macaza Institution, a stand-alone medium-security facility with an inmate capacity of 240.

In the late '80s and '90s, Bernardo committed a series of sex crimes, rapes, and murders in Toronto.

His wife, Karla Homolka, joined him and became his accomplice in the '90s and the two videotaped their crimes. They were dubbed the "Ken & Barbie killers" in the media because of their looks.

Ontario's Ministry of the Attorney General reports that between May 1987 and December 1992, Bernardo raped or sexually assaulted at least 18 women and teens in Scarborough, Peel, and St. Catharines and killed three teens in St. Catharines and Burlington.

The couple kidnapped, sexually assaulted, and murdered Kristen French, 15, Leslie Mahaffy, 14, and Tammy Homolka, 15.

On Monday the CSC issued a statement saying it acknowledged that its decisions have an impact on victims and that it regrets "any pain and concern this has caused."

It went on to say that CSC Commissioner Anne Kelly has ordered an "additional review of this offender's security classification to ensure it was appropriate, evidence-based, and more importantly, adequately considered victims."

The CSC added that at any point, an inmate can be placed or returned to a higher security level if deemed necessary to ensure the safety of the public or our institutions.

Pending the review that has been ordered, the CSC stated that it "will not hesitate to do so if needed."