"What exactly part of this is criminal? " The part where you commit obstruction of justice by identifying which people are cops and hiding the law-breaking from them while you know they are investigating.

(and you do it because the law-breaking is benefiting you).

Uber would have been significantly better off, legally, actually and clearly refusing service instead of deliberately misleading them.

If the cops come by, and ask you where your friend stashed the murder weapon, and you refuse to talk to them - probably defensible

If the cops come by, and ask you where your friend stashed the murder weapon, and you say "3000 miles away in a storm drain" to deliberately mislead them, congrats, there are plenty of jurisdictions where you have committed obstruction.

If every time they come around, you deliberately cover the spots with blood and the murder weapon hiding spot, ....