Testifying at the sentencing hearing for Vincent Walkem on Thursday, a doctor called for universal HIV testing because he believes a large percentage of people do not know they are infected with the virus.

Walkem, who is HIV positive, was identified by police in 2004 as a suspect in a case of infecting a woman with the virus by having unprotected sex with her. He pleaded guilty to two counts of aggravated sexual assault.

Dr. Brian Cornelson called for "universal testing" because he believes thousands of people in Canada have contracted the virus but do not know it.

"I think that testing for HIV is a good idea," Cornelson told the Toronto Star. "Probably about a quarter of people who are HIV positive don't realize it."

He said that anyone having sex with an HIV positive partner has a 1 to 3 per cent chance of contracting the virus.

"It's like playing Russian Roulette. The more times you do it, the greater the risk you'll acquire the infection," Cornelson said.

Walkem was 28 in 2004 and knew about his HIV status. He had a sexual relationship with an 18-year-old woman and reportedly ignored the advice of health officials to warn his sexual partners and use protection.

One of the victims subsequently tested positive for the deadly virus. The second victim has tested negative.

The identities of both women have not been revealed.

Walkem took the stand Friday afternoon in his own defence. He admitted to deliberately trying to infect women with the virus by having unprotected sex with them.

Asked why, Walkem replied that he did not think about it.

"There's nothing I can say that can justify it. I wish it never happened," Walkem said. "I hope in the future to seek counselling to figure out why I made these terrible decisions."

Justice Arthur Gans quickly replied to Walkem's statement, saying it sounded "hollow."

"Is there any reason why you didn't seek counselling since your arrest?"

Walkem had no reply for Gans.

Prosecutor Mary Humphrey is looking for an eight-year jail sentence for Walkem. His lawyer, Graham Clark, said his client's guilty plea shows that Walkem is "taking responsibility," the Star reported.

Walkem will return to court in two weeks for sentencing.

With a report from CTV's John Lancaster