You know, this worry that illegals won’t report crimes or be witnesses is a poor rationale.
The more illegals you remove from the community, the more the witnesses will be legal residents with no worries about deportation. Illegals must make terrible witnesses anyway as they can be blackmailed, threatened or disappeared by criminals; or get deported at any time by ICE and throw out the court case that relied on their testimony. No LEO should want to have to rely on them.
You broke the code! This has been a nonsensical argument to try and BS the populace into thinking this is an important LE aid. You keep illegals from being identified and removed, and you keep your crime rate higher than it would be otherwise.