He hadn't been charged. The shooting was less than a week before, and through the investigation the car he was in was seen heading to and fleeing the scene.
Kaba, alongside a few other known gang members, were known to drive the vehicle, and the intelligence suggested he may have been the gunman.
This was why the car had a marker on it. This is why the stop was authorised, for as you say, he needed to be taken into custody for a prompt investigation.
It's also why the driver of the vehicle perceived a risk to the public, and not merely the police. Based on all evidence available, he'd have got a lengthy custodial.
Which would explain why he tried to ram his way out, to avoid arrest and a potential lengthy jail sentence.
