An Ontario court has declared another plank of the Conservative government's tough-on-crime agenda unconstitutional.

Ontario Superior Court Judge Alan Bryant struck down a section of the Criminal Code introduced in 2008 dealing with dangerous offenders in a decision published Tuesday.

The ruling comes in a year during which judges in Ontario have already struck down two mandatory minimum firearm penalties from the same "Tackling Violent Crime" omnibus law.

Traditionally the Crown had to prove several requirements before someone is designated a dangerous offender, including a pattern of dangerous behaviour or likelihood of causing pain through a failure to control sexual impulses.

Dangerous offenders — sex killer Paul Bernardo is designated as one — can be given indeterminate sentences and be locked up for life.

What changed in 2008 was that the new provision provided a shortcut of sorts for the Crown in a small subset of cases.

If an offender was convicted three times of a specified violent or sexual crime with sentences of at least two years the burden of proof shifted from the Crown to them.

All the Crown had to prove was that the offender was convicted of those offences and was sentenced to at least two years. The offender then had to try to prove that they did not have a pattern of dangerous behaviour.

That burden is too onerous, lawyer Peter Behr argued — and Bryant agreed.

"[The law] reverses it and puts it on the accused to say, 'You're real bad and we're going to put you away, you're likely to be put away forever, unless you show otherwise,"' Behr said in an interview from his office in London, Ont.

Behr represents Roland Hill, the man at the centre of this constitutional challenge. He was convicted in 2000 of a sexual assault and in 2004 of assault causing bodily harm.

In the case now before the courts, Hill pleaded guilty to two counts for what Bryant called a "horrible" assault on a "defenceless young woman."

Reverse onus violates charter, court rules

Bryant found that the reverse onus violates the charter, but that the Crown proved Hill was a dangerous offender through the traditional method.

The case returns to court Oct. 16 to set a date for sentencing — judges have discretion to give a dangerous offender an indeterminate or a fixed sentence.

As the matter is still before the courts, a spokesman for the Ontario Ministry of the Attorney General said he could not comment beyond noting the rest of the dangerous offender sentencing regime is not affected by the ruling.

The Crown had argued that the provision streamlined the process for dangerous offender designations only for the worst of the worst.

"I do not accept the Crown counsel's submission that there is a pressing need to streamline the process for labelling a small class of individuals as dangerous offenders," Bryant wrote.

Between 1978 and April 2005 there were 384 people who were designated dangerous offenders.

"A breach of an individual's [charter] rights cannot be justified or condoned in a free and democratic society because the class of affected individuals is small," Bryant concluded.

The Crown had no evidence showing that the reverse onus was necessary to make sure the most dangerous offenders are designated as such, Bryant wrote.

Crown lawyers can access all kinds of evidence to prove their case such as psychiatric assessments, police witnesses and criminal records, he noted.

The dangerous offender reverse onus was part of the government's 2008 Tackling Violent Crime bill, which increased penalties in a number of areas, including gun control, drunk driving and the age of consent.

In July, an Ontario Court judge struck down a three-year firearm trafficking mandatory minimum sentence in the case of a crack dealer who offered to sell an undercover police officer a gun.

In February, Ontario Superior Court Judge Anne Molloy struck down a three-year minimum sentence for a first offence of illegally possessing a loaded gun.

The cases are expected to be appealed to higher courts. The Ontario government has already indicated they will appeal the Molloy decision.