Police in Seattle allege Michael Stanley met the teen at a west-side grocery store early Tuesday and walked with him to a nearby alley, where the man had apparently been sleeping.
"That's when Stanley supplied this kid with alcohol and then he attacked him," said police spokeswoman Det. Renee Witt.
"The teen was armed with a knife. He pulled the knife and fought Stanley off. He ran away."
Witt said a resident who heard the commotion shouted out his window to ask for quiet. Stanley yelled back and threatened to assault the person, she said.
Officers responded and arrested Stanley for harassment. A news release said Stanley was combative and appeared drunk. It also said he was carrying a knife.
Witt said officers were soon able to determine Stanley's identity. "And during the course of their investigation, that's when the teen victim approached and told the officers what had happened to him."
She said the boy wasn't injured and was "about as good as anybody can be under the circumstances."
Prosecutors will be deciding what charges Stanley could face, she added.
Stanley entered the United States earlier this month as Canadian police were searching for the 48-year-old. On Oct. 1, the electronic monitoring bracelet he had been wearing was cut off and found on the roof of a business in Lloydminster on the Alberta-Saskatchewan boundary.
He was being monitored by police under a peace bond with conditions, including one ordering him to stay away from children.
His criminal record in Canada dates back to 1987 and includes sex offences against an elderly woman and two mentally challenged boys.
When Canadian police discovered he was missing, they issued a public alert, which described the Edmonton man as an untreated, violent sex offender. Soon after, several schools in Saskatchewan locked their doors after unconfirmed sightings of Stanley.
A few days later, he crossed into Blaine, Wash., south of Vancouver.
Edmonton police said they had warned U.S. authorities that he might try to cross the border, but officials allowed him in after determining he was an American citizen and not the subject of an extraditable arrest warrant.
Alberta Justice had started the extradition process, then announced it would not seek to have Stanley returned to Canada because the charges he was facing at the time — breach of recognizance, mischief and driving charges — didn't involve violence.
A Canadian extradition expert had publicly suggested Canada should say "good riddance" and leave Stanley in the U.S. because extradition would be costly and he would face little time behind bars if convicted of the minor crimes. But Alberta's official Opposition Wildrose party called the government's decision "morally reprehensible'' and demanded justice officials try to get the sex offender back.
A spokesman with Alberta Justice had no comment Tuesday on Stanley's arrest. Wildrose justice critic Shane Saskiw repeated that Stanley should have been extradited as soon as possible to protect all people — regardless of whether they live south or north of the border.
"We were afraid that an incident like this would happen," said Saskiw, who added that the good news is that Stanley is now in custody in the U.S. and, if charged and convicted, could end up in prison again.
"I think he's going to find that the justice system there is very, very harsh and I hope that he's put behind bars for a long time."
Seattle police located Stanley in the city last week and, as a registered sex offender in Canada, he was told he also had to register in the U.S. He listed his address as one near a preschool and just a block away from Pike Place Market, a scenic downtown destination for both tourists and locals.
A local TV station, KIRO-TV News, tracked down Stanley. In an interview he said he'd had enough of Canada for making him look like "some creep, some pedophile." He denied committing any offences north of the border.
He said he wanted a fresh start and had no intention of committing any crimes.
"You can walk down the street with me, but you're not going to catch me doing anything," Stanley said.
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