IMO The prosecution will appeal to the common sense of the jury. While most juries do use common sense, I admit there was a recent case in FL where common sense was thrown out the window. I hope that was just an aberration.
To consider it normal for ANYONE to make a habit of following absolute strangers belies common sense. Normal people just do not do that. I doubt that any jury in the world would debate the absurdity of this. It is on it's face absurd and requires no debate. Common sense tells me that a jury would not consider running after a stranger for no apparent reason as normal. Therefore they will consider the reason GZ either followed by walking or ran after TM. Common sense demands recognition that GZ did this for the purpose of detaining TM because "These *advertiser censored**h*les always get away." A reasonable person would recognize that GZ was unable to carry out his plan to detain TM because TM resisted, and so he killed him. I don't think the judge will allow the defense (should they try) to blame TM because he didn't get home as quickly as some believe he should have. That's just utter nonsense and denies TM his freedom of movement, albeit posthumously.
What GZ did cannot be excused under any logical reasoning, and I think the prosecution will point that out to a jury which, hopefully, will use its common sense.
I believe that following someone with the intent to harrass them, imprison them, or harm them in any way is illegal and GZ should be made to pay for his actions. Because, IMO, that is exactly what he did.
And unless GZ can produce medical records showing he had a common sense reason to fear for his life or fear he would be seriously injured, (And not an "enhanced" version of a video or a dubious photo of an unidentified person with very minor puncture wounds on the back of his head,) self-defence or SYG is a non-starter.
In fact, a jury must decide using the criteria of what a "Reasonable person," would conclude. GZ's contention of necessity of killing TM, and if we use the the limited evidence which we now know, is not reasonable to a person with common sense.