How did ICE know where to look? (see details)

Every day since President Trump took office, ICE has been arresting tons of criminal illegal aliens. Thousands in just a few days. From what I’ve seen, ICE is going right to where the criminals are living or working and just arresting and/or detaining them.

That is a huge number to impact if they are having to do investigations to find these people and to know they are criminals. So how do they know where these people are? Was all this information available to Biden’s administration and they purposely let the criminals stay in this country? Or is this current effort being driven 100% from tips and whistleblowers?