At usual, some of you guys beat me to it. Isn't there enough red meat to take on or investigate in Chicago, rather than doing these petty crumb motor vehicle offense interactions? Unless, of course, they knew something about this kid that's not been revealed yet.
He had several gun related charges and was IMHO was suspected of repeating them. Good show clip with Megan Kelly here:
Officer-Involved Shooting in Chicago Becoming Major Media Story, with Viva Frei and Phil Holloway : https://www.youtube.com/watch?v=VtTeGeMEOb4
Really does look like the occupant started shooting, and yes, he KNEW they were cops!
They had a tip about the dude and they needed something like probable cause to make contact. So...seat belt violation. It’s sketchy, but it’s done a lot. And usually with a great deal of success.
CC