DENVER -- A statewide sting operation is under way targeting Colorado's top 100 sex offenders and other fugitives wanted for sex related offenses.

Operation Shepherd is a joint effort by the U.S. Marshal's Service, Colorado Bureau of Investigation, Department of Corrections and local police departments and sheriff's offices.

So far, the sting has netted 83 arrests.

"Our mission is to go after sex offenders," said Adam McGovern of the marshal's service. "We're looking for individuals who have failed to register and those who have outstanding warrants for various sexual crimes."

The task is daunting.

A 7NEWS crew followed one team as they drove from Denver to Thornton and then to Englewood and Wheat Ridge looking for fugitives.

When officers asked a woman at an apartment in Thornton where her son was, she told them she didn't know.

"What's his phone number?" they asked.

"I don't know," she responded.

So officers knocked on a neighbor's door and showed the tenant a picture of the fugitive.

"Have you seen this man? they asked.

"I don't know," she responded.

It was the same story in Englewood.

Officers followed up on a tip about one of their suspects and tracked him down to an apartment on the 1200 block of Corona in Denver.

"We just contacted one that has a sex assault on a child warrant out of Arapahoe County," said Matt Menck of the Department of Corrections. "So we placed him in custody."

Neighbors told 7NEWS they were glad officers made the arrest.

"I have my nieces that come and visit me," said Blake Bradley. "So it's good to know that we've got one less of those people on the street."

McGovern said it's difficult to track down the unregistered sex offenders.

"Nobody wants them to live in their house, so they stay in a shelter," McGovern added. "Recently a big shelter closed, so that leaves a lot of offenders with no permanent address. We don't know where they are."

The Marshal's Service is asking for help tracking down the unregistered offenders.

If you know of any unregistered sex offenders in your neighborhood contact the U.S. Marshal's 24-Hour Hotline at (303) 335-3400. To see the list of Colorado's Top 100 Most Wanted Sex Offenders go to Metro-DenverCrimestoppers.com