Because companies like Canon sell multi-thousand dollar cameras and attachments to police agencies that are designed to make sure photographs can't be tampered with so that they're admissible in court. There can't be the possibility that a rogue cop altered a photograph, or the case can get thrown out.

It's why the cameras police departments use cost 5x more than the consumer versions.

I'm not sure "government agency buys expensive thing" is proof of actual need of said expensive thing. And even if it were, it's not clear to me that the need applies in this case.