Washington State Patrol spokesman Dan Coon said with no warrant, troopers and other local officers can't arrest Stanley.
"That's the issue, unless he does something to make us arrest him," he said, adding "The question is how he got through the border."
Coon said troopers had not had any contact with Stanley, but couldn't speak to county and local authorities.
Stanley has a long history of sexual offences against women and children and has been missing since Oct. 1 when the electronic monitoring bracelet he was wearing was cut off and found in Lloydminster, on the Alberta-Saskatchewan boundary.
Last week, schools in several west-central Saskatchewan communities locked their doors and kept children inside after police got multiple, unconfirmed sightings of the Edmonton man.
He's wanted in Canada on charges of breach of recognizance and mischief and driving offences, but he isn't wanted in the United States, so Hayduk said police have no authority to arrest him.
"The extradition process we are still exploring those options," he said.
Hayduk said officers do know Stanley's specific whereabouts, but he wouldn't release those details.
"We can take some comfort that police know where he is and will be taking the appropriate steps to ensure the communities remain safe."
Hayduk said there is no evidence that Stanley has re-offended while he has remained elusive. "At this point it looks like he was just fleeing from us," he said.
Stanley was released from jail 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 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.