Authorities typically obtain an administrative warrant giving them permission to detain a person for violating immigration law.

ICE agents can arrest people they discover to be in the U.S. illegally while searching for people on their target list. People who answer ICE agents’ questions about someone else sometimes end up arrested themselves. In one case in Houston last year, a young father of five was arrested in the parking lot of his apartment building after ICE agents asked him about people who lived nearby, then demanded his identification and eventually detained him.

These “collateral” arrests can comprise a large portion of the arrests in any operation. In one December 2017 operation in northern Kentucky, just five of the 22 arrests ICE made were of people it originally targeted, according to agency documents released under the Freedom of Information Act.

WHAT WE’RE EXPECTING NEXT

The Washington Post and Miami Herald reported that 10 cities are expected to be targeted in raids starting Sunday. The Herald reported those cities are Atlanta, Baltimore, Chicago, Denver, Houston, Los Angeles, Miami, New Orleans, New York, and San Francisco.

ICE officials said this week that they had sent about 2,000 letters in February to people in “family units” who had already received final orders to leave the country. The people who received those letters may be the targets of the enforcement operation.

Acevedo, the Houston chief, said ICE officials this week declined to provide him with any information about the expected weekend operation besides saying they had ongoing enforcement operations. He criticized President Donald Trump’s tweets Monday saying that agents would begin removing “millions of illegal aliens.”

“It instills fear,” Acevedo said. “We rely on the cooperation of that population to keep all Americans safe, all residents safe, and all members of society safe. … When you say you’re going to go arrest millions of people, that has a chilling effect on the cooperation.