Zimmerman was specifically told not to follow the kid, he did anyway
Nitpicking here, and I haven't really followed this case since it initially happened, but the bolded is not quite accurate.
IIRC, the language used by the 911 operator when Zimmerman said he was following Trayvon was "kay, we don't need you to do that."
Which, to rational individuals, the implication is clear for him to stop fucking following him, but if one's perspective is a bit skewed, it could be perceived (and likely argued in court) as "okay, you don't
need me to do that, but I'm just so gosh-darned motivated and helpful that I will keep following anyway. Don't want him to get away, after all."
I'm not defending Zimmerman, it's bullshit for him to follow either way, but "we don't need you to follow him" != "Don't follow him". One would be a clear direction, the other comes across as a suggestion.
Of course, if I'm mis-remembering the 911 operator's spiel, then disregard anyway.