One of the many scenarios I've considered and scrutinized for plausibility is that he was "following" TM to keep an eye on him and see where was going so he could tell the cops the direction TM was heading. He could say that he never intended to confront TM. Unfortunately, IMO, this scenario (based on the scant evidence we have) is plausible. I'm not saying it's the truth, but it does provide a reasonable explanation for GZ leaving his car.
IIRC, GZ never mentions wanting to "catch" TM or wanting to harm the suspect. IMO, there is no intent to harm TM evident in the transcripts that have, so far, been released to the public.
JMO, OMO, and :moo: