Here is what I think MIGHT have happened. Our house sits on a little hill right above the community pool. And there have been some break-ins there at the pool, and some costly vandalism. Also, some people sneak in after the pool is closed to party and midnight-swim. Since my own kids used to do that in high school [ I think so anyway] I do not usually report this even though my German Shepherd alerts me to any strange occurrences there.
But when I have seen people lurking, dressed in hoodies and in dark clothing, and standing in the shadows, then YES, I call the non-emergency number.
GZ first reported that TM was under the awning at the community center. That is a likely spot for a burglary or a break-in. So GZ probably thought he had a potential burglar and so he was going to cling on to this kid, hell or high water.
He was wrong and made terrible decisions. But I do not believe he set out to murder anybody, imo. I think this was the perfect storm of horrible circumstances. Especially weird if TM was already safely on his back porch,and then went to confront GZ, imo.