A violent sex offender who recently fled Canada and was arrested Tuesday after yelling a threat in an alley is suspected of sexually assaulting a 16-year-old boy earlier in the day, police said.

Michael Sean Stanley met the boy at a west Seattle grocery store, struck up a conversation and walked with him to an alley where police say he plied the teen with alcohol. Stanley grabbed the teen and sexually assaulted him, police said.

The 16-year-old pulled a knife and was able to run away and contact police.

Detectives believe the incident happened before police received several calls about noise in an alley and Stanley threatened someone who asked him to be quiet.

When police arrived, Stanley became combative and said he had a knife. He appeared intoxicated, according to authorities. He was arrested and jailed for investigation of the assault threat.

An American citizen, Stanley crossed the border and was located in the Seattle area last week. Canadian officials decided not to seek extradition.

He registered as a sex offender with the King County sheriff's office and listed his address as an intersection just a block away from Pike Place Market, a scenic destination for both tourists and locals. It's also near a preschool, even though he had been ordered to stay away from children in Canada.

There was no reason to arrest Stanley earlier since Canada hadn't pursued an extraditable warrant and he wasn't wanted for any crimes in the United States, authorities said.

Stanley was released from jail in Canada in April 2011 after completing a 32-month sentence for assault and forcible confinement.

Stanley was being monitored by police under a peace bond, which Canadian authorities can get to impose conditions on individuals in the community. His peace bond has 20 conditions, including one ordering him to stay away from children.