Throughout the Trump administration's ongoing immigration enforcement effort in the Chicago area, federal authorities repeatedly have said they're targeting the worst of the worst. But the government's own data reveals only 15% of those detained had a prior criminal conviction, and only 3% have convictions for violent crimes.

CBS News Chicago has asked the head of U.S. Immigration and Custom Enforcement operations in Chicago, filed Freedom of Information Act requests, and asked Homeland Security Secretary Kristi Noem about who has been arrested during Operation Midway Blitz, and why.

ICE's own data paints a picture that it's not just convicted criminals who are being taken into federal custody. 

New numbers released by ICE to the Deportation Data Project and analyzed by CBS News showed that, of those detained in Chicago or Broadview from the start of Operation Midway Blitz through Oct. 15, only 15% of those people have a criminal conviction. Another 18% have pending criminal charges. The vast majority, 67%, have only civil immigration violations such as overstaying a visa or crossing the border illegally.

"The number of arrests in total skyrocketed starting when [President] Trump returned to office, but particularly the group that has seen the largest growth, especially in recent months, is those with only civil immigration violations. So, no pending criminal charges or convictions," said Julia Ingram, a CBS News data journalist.

Ingram noted it's not clear what pending charges any of that 18% are facing, based on what ICE has released. 

"One of the things that's missing is the severity of the charge when a person has a criminal charge, but not a criminal conviction. We have insight, when there's a conviction, into what the most serious conviction was, and what we're seeing is in that case, across the whole universe of data, about 7% of people have convictions for violent crimes," Ingram said.

While 7% of those detained nationwide under the Trump administration's immigration crackdown have prior convictions for violent crimes, in Chicago, during Operation Midway Blitz, that figure is only 3%.

In October, CBS News Chicago asked Noem about the identities of the thousands of people who've been arrested, noting that at that point, the government had only identified a few hundred of those taken into custody.

"Oh, we can get that for you. Those are individuals that have been detained, that we've interacted with, that were here illegally, committed crimes, or had final orders of removal issued against them," Noem said.

But more than a month later, Homeland Security still has not identified every person arrested during Operation Midway Blitz. DHS representatives said they're still working on that information.

CBS News Chicago also is still waiting for a response to a FOIA request regarding Operation Midway Blitz arrests.

"They have 20 business days to respond to a request, and under certain circumstances, they can extend that to 30 working days, but they're not complying with those timelines. They are literally violating the law," said Raul Pinto, deputy legal director for transparency at the American Immigration Council.