Prime Minister Stephen Harper said Thursday he was upset to learn that a convicted murderer spending life in prison is receiving more than $1,100 per month in old-age benefits, and he plans to "rectify" the situation.

Last week, it was reported that Clifford Olson, who is serving a life sentence for killing 11 boys and girls between the ages of nine and 18, has been receiving the payments from the federal government.

"This is a situation that has many, many Canadians upset and for good reason," Harper said in London, Ont. "I've instructed the minister to look into what options are available to us to rectify this situation because it should be rectified."

Harper said it's uncommon for a senior citizen to be serving a life sentence for heinous crimes, which is likely why the issue hasn't arisen in the past.

But he said that doesn't mean the status quo should continue, and that he has asked Human Resources Minister Diane Finley to look at ways to exclude prisoners from the pensions system.

"Obviously I've read all the stories recently in the paper about Mr. Olson and I must admit that I'm as upset about this, as concerned about this as any other Canadian is," Harper said.

Olson, who turned 70 this year, confessed to his crimes in 1982. He has shown no remorse for the murders and has even claimed to have committed dozens of other murders for which he was never caught.

As a senior, he qualifies for Old Age Security and Guaranteed Income Supplement. That money has been going into a trust fund for Olson, who is serving 25 life sentences at a maximum security prison.

Sharon Rosenfeldt, whose son Daryn was murdered by Olson in 1981, said she was "shocked" to learn the convicted killer has been collecting public benefit payments.

"It certainly did take me aback because I had no idea this was happening in Canada," Rosenfeldt said on CTV's Power Play.

She said she thought Olson should return the money he has received. The money, she said, should go to "people with disabilities, pensioners, veterans, who actually contributed and put money into the fund."

But Craig Jones, executive director of the John Howard Society of Canada, cautioned against making changes to the law based on Olson's case.

"Using extraordinary cases to smuggle in changes to criminal justice policy is a practice that I think Canadians should be rightly skeptical of," Jones said.

"Every lawyer will tell you that bad cases make bad law," he added.

With files from The Canadian Press