(NewsNation) — There are accused and convicted criminals living in the United States illegally, and it’s up to U.S. Immigration and Customs Enforcement to track those people down — a difficult task made harder by sanctuary policies in some areas.

ICE’s targets are not just any undocumented immigrants, but those the agency deems public safety threats.

“Public safety threats are the people that are a problem,” Chicago acting field office director LaDeon Francis told NewsNation. “They’re the ones that you don’t want back into the community.”

NewsNation national correspondent Alex Caprariello spent two days riding along with the elite Enforcement and Removal Operations team in Chicago as they conducted surveillance and arrests of undocumented immigrants with criminal records.

During the ride-along, Caprariello witnessed arrests of undocumented immigrants heading to restaurant jobs and providing home health care — people surrounding Americans at work and even allowed into their homes.

The biggest challenge facing ICE’s efforts is a lack of cooperation and information-sharing from some local police departments and state governments with “sanctuary” policies limiting such assistance.

“There is a level of protection for these (individuals) that (enables them) … to blend in and hide with just your average immigrant, which multiplies the amount of work and efforts that we put into it,” said Ray Hernandez, assistant field office director for ICE’s Chicago office. “These are sensitive locations that these migrants are living in. And then they hide within these groups, and they conduct criminal activity within these shelters. And ERO (Enforcement and Removal Operations) is not allowed into those communities.”