Here's what I think, FWIW...
I think he WAS out stalking his prey. His prey being those imagined A$$**le thugs that always got away. And I believe he does have a propensity for racial bias - so that makes him a racial predator, IMO. He called the police so that when the 'suspect' was arrested he would be hailed as a hero and savior in his world and little 'kingdom'. Once again, the 'suspect' was getting away and he wasn't about to let that happen so he went after him. I think he caught up to him and most likely grabbed him trying to 'detain' him and Trayvon fought back and he shot him being the coward he is.
So while I don't think he started off his day by deciding he was going to kill someone, I believe he is a racial predator and I think there was definitely premeditation and intent.
That's my opinion.