Harper also promised a national, online database accessible to the public listing the names of high-risk child sex offenders, to replace a patchwork of existing databases.
"We do not understand why child predators do the heinous things they do and, in all frankness, we don't particularly care to," Harper said in Richmond, B.C., as dozens of Canada Border Services Agency officers stood behind him.
"What we do understand is that there are some terrible people out there, criminals of the worst kind, and that they must be dealt with."
Harper said that the measures will be included in the Conservatives' Tougher Penalties for Child Predators Act to be introduced in Parliament this fall.
That legislation would require convicted sex offenders, parole and probation officers to notify police in advance of international travel plans, and authorize police to inform Canadian border guards who can — "where appropriate" — alert destination countries that a dangerous offender is coming their way.
"Just as we must protect Canadian children, we should do what we can to protect innocent kids beyond our borders," Harper said.
The national registry would include the names of high-risk child sex offenders who have been the subject of local or provincial public notifications.
The proposed changes would also include measures to improve information sharing between police and border officials in order to track sex offenders.
Harper cited the case of Howard Cotterman, a registered American sex offender who had been returning to the U.S. after a vacation in Mexico in April 2007.
A forensic examination of Cotterman's laptop revealed hundreds of images of Cotterman molesting a young girl and he was arrested.
"Cotterman was apprehended basically though information sharing," Harper said. "However, if Cotterman were Canadian, under our current practices this might not have happened.
"Gaps in information collection and sharing, as well as gaps in enforcement, mean child predators can slip over our borders unmonitored. That is going to change."
It's unclear, however, how Canadian border officials would have missed a similar case.
According to reports, U.S. border agents found Cotterman's name on a national database as a sex offender for a 1992 conviction for sexually assaulting a minor.
They retrieved from his car two laptop computers and three digital cameras, and undertook a forensic examination of the devices. After breaking the password protection on his laptop they found 378 images taken over several years, most of them showing Cotterman sexually assaulting a girl between 7 and 10 years old.
A district judge suppressed the evidence, finding it violated Cotterman's protection against unreasonable search but a federal appeal court upheld the seizure and search.
Brian McConaghy, a former RCMP child predator investigator and founder of the charity Ratanak International, welcomed the changes.
McConaghy, whose charity rescues and offers rehabilitation for children exploited in Cambodia, said Canadian predators all too often find their victims in countries without the resources to combat their crimes.
"There's not efficient policing, there's not social services, there's not supportive families so these predators go overseas to find the weakest link and the most vulnerable children," he said after watching Harper announce the measures.
"Slowly but surely we're whittling away at the various loopholes they can use to have freedom to move around."
Vancouver Police Chief Jim Chu and Victoria Police Chief Jamie Graham were also among the crowd at Monday's announcement, along with Tom Stamatakis, president of the Canadian Police Association.
Stamatakis thanked the prime minister for the new measures and for previous amendments that, among other things, created minimum sentences for the assault of a child under 16 and made it illegal to use a computer to communicate with a child for the purpose of committing an offence.
"With these measures, the message to those who prey on children is clear: This future legislation will be part of a well-co-ordinated assault on their abilities to exploit our children, our most vulnerable members of society."
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