JENKS, Oklahoma - There are 425 registered sex offenders in Tulsa County, and it's up to local law enforcement to keep tabs on them.

That's where the U.S. Marshals step in to help.

The 425 sex offenders aren't all on the same level.

Monday, U.S. Marshals checked in on the Level 3 offenders, which is the highest level of sex offender, meaning their crimes are considered the most heinous.

It was an unexpected house call for several registered sex offenders in Jenks and Bixby this morning.

The U.S. Marshals and local police checked up on each offender in the area one by one.

"We try to do it as much as possible because the more you do this the more these offenders know they're being monitored," said U.S. Marshals Senior Inspector Dustin Ramsey.

Ramsey has been chasing after child predators in Northeastern Oklahoma for the past year.

"The ones that we're checking, they're child rapists, child molesters, child pornographers...a history of violence towards children," Ramsey said.

Ramsey said most of the offenders in this area are good about checking in.

While most of the compliance checks went without a hitch, some could turn into problems.

Like an offender registered to a house in Jenks. From what Ramsey can tell, the offender never moved in.

Notes were left on some doors letting the offenders know police had been by and to check in ASAP.

Ramsey said they try to catch people when they're home and try to get a look inside.

"Sometimes these guys will have child porn laying out, they'll have computers when they're not supposed to. So, anything a sex offender should not have is basically what we're looking for," Ramsey said. 

And if you think this was done the week before Halloween trick or treating by coincidence, think again. 

The U.S. Marshals want offenders to know they'll be watching.

There are 44 Level 3 sex offenders in all of Tulsa County.

The Marshals said if your child is trick or treating this year, check out the sex offender registry online and avoid those houses.