An Edmonton sexual assault case is at the centre of an argument about the constitutionality of Canada's sex offender registry.

The Court of Appeal of Alberta heard submissions Wednesday about whether a judge should have discretion about placing an offender on the registry, as well as whether or not placing anyone with more than one sexual offence conviction is a violation of charter rights.

The offender in question has long since served his time. In 2011, Eugen Ndhlovu attended a party where he sexually touched two women.

He pleaded guilty to two counts of sexual assault, and was handed a six-month jail sentence with three years probation. He was found to be at a low risk of reoffending, but because he has more than one conviction, he was to be automatically placed on the national sex offenders registry for life.

The mandatory placement came into effect through changes to the Criminal Code enacted by then-prime minister Stephen Harper's government in 2011.

Ndhlovu appealed to Court of Queen's Bench, arguing that the amended rules are unconstitutional because the automatic lifetime placement for anyone convicted of more than one sexual offence is too broad and grossly disproportionate.

He also argued judges should have discretion about placing offenders on the registry. The judge who heard his case agreed, and struck down the 2011 changes.

But Alberta's Crown prosecution disagreed, and sought to overturn that decision in arguments before the Alberta Court of Appeal on Wednesday.

Crown appellate counsel Jason Russell argued the Harper government's changes to the rules help make the registry a better tool for police. If it's not a comprehensive list of people with these types of convictions, it's not particularly helpful to investigators tracking down possible suspects, he argued.

He also took issue with the suggestion that including low-risk offenders on the registry is casting too wide a net, arguing they are more likely to commit another sexual offence than a member of the general population.

"There is no way of knowing which of these offenders is going to reoffend," he said.

Ndhlovu's lawyer Elvis Iginla countered Russell's submissions, saying that after a number of years, low-risk offenders likelihood of recidivism drops to that of the general population.

He said it's not right to place every offender with more than one conviction on the list for life and argued the court should weigh the risk to public safety with the individual's right to liberty.

"It just paints everybody with one brush," Iginla said.

The stakes of the case also drew interest from outside the province. The HIV & AIDS Legal Clinic Ontario and the Canadian HIV/AIDS Legal Network gained intervenor status in the case.

The groups' lawyer Matthew Gourlay spoke briefly during the hearing, arguing that the current rules around placing people on the registry are grossly disproportionate in cases where an HIV-positive person picks up an aggravated sexual assault conviction for failure to disclose their status to a sexual partner.

The appeal court reserved its decision in the case.