Because he didn't should not have been a lawful excuse for shooting him. His killer playing cop himself is the guy who should have called police.
Zimmerman did call police and was walking back to meet them as he was told to do... and got attacked by Martin u stupid fuck
He called police and did what police told him to do and was attacked
George Zimmerman calls to report a suspicious character
Zimmerman: Hey, we've had some break-ins in my neighborhood, and there's a real suspicious guy-- it's Retreat View Circle. The best address I can give you is 111 Retreat View Circle. This guy looks like he's up to no good, or he's on drugs or something. It's raining and he's just walking around, looking about.
Dispatcher: Are you following him?
Zimmerman: Yeah.
Dispatcher: Okay, we don't need you to do that.
Zimmerman: Okay.
Dispatcher: Alright, sir, what is your name?
Zimmerman: George. He ran.
Dispatcher: All right, George. What's your last name?
Zimmerman: Zimmerman.
Dispatcher: And George what's the phone number you're calling from?
Zimmerman: [redacted]
Dispatcher: All right, George. We do have them on the way. Do you want to meet with the officer when they get out there?
Zimmerman: Yeah.
Dispatcher: All right, where you going to meet with them at?
Zimmerman: If they come in through the gate, tell them to go straight past the clubhouse. And uh, straight past the clubhouse, and make a left. And then they go past the mailboxes, that's my truck... [unintelligible]
Dispatcher: What address are you parked in front of?
Zimmerman: I don't know. It's a cut through, so I don't know the address.
Dispatcher: Okay, do you live in the area?
Zimmerman: Yeah, I... [unintelligible]
Dispatcher: What's your apartment number?
Zimmerman: It's a home. It's 1950-- Oh, crap. I don't want to give it all out, I don't know where this kid is.
Dispatcher: Okay, do you want to just meet with them right near the mailboxes then?
Zimmerman: Yeah, that's fine.
Dispatcher: All right, George. I'll let them know to meet you around there okay?
Zimmerman: Actually could you have them call me and I'll tell them where I'm at?
Dispatcher: Okay, yeah, that's no problem.
Zimmerman: Should I give you my number or you got it?
Dispatcher: Yeah, I got it. [redacted]?
Zimmerman: Yeah, you got it.
Dispatcher: Okay, no problem, I'll let them know to call you when you're in the area.
Zimmerman: Thanks.
Dispatcher: You're welcome.
http://law2.umkc.edu/faculty/projects/ftrials/zimmerman1/zimcalls.html
So u stupid fuck Zimm called police did what he was told, Martin double backs and attacked Zimm