Martin's girlfriend said he told her somebody was following him. She told him to run. He said he wasn't going to run, just walk fast. A little later, she heard Martin say, "Why are you following me?", and another voice asked "What are you doing around here?" Then there was a scuffle, and the call dropped. The call ended at 7:12 pm, and the cops arrived at 7:17 to find Martin dead.
We do not know when Zimmerman pulled his gun ~ nor do we know how far away he was from Martin when he fired. Such things have not been revealed.
Earlier there was an article posted by Massad Ayoob, a well-known firearms and self-defense instructor. He reports that the condition of the gun is consistent with a struggle over it:
The death weapon was a Kel-Tec PF9 semiautomatic 9mm pistol. It has been reported that the gun was recovered with a full magazine and that only the chambered round had been fired. This is a condition we associate with something preventing the gun from cycling a fresh round from the magazine into the chamber after the shot was discharged. One thing that can cause that is another man’s hand wrapped around the pistol, retarding its slide mechanism. This would indicate, as could certain gunshot residue patterns or cuts in certain places if found on Trayvon Martin’s hand(s), that a struggle for a gun was taking place when the fatal shot was fired.
There are a lot of things the cops haven't told anybody. I presume they'll be telling the grand jury about it.
That would suggest that Zimmerman had the gun out, possibly hoping to make an arrest without a struggle. It would also explain why Martin might have been so intent on beating Zimmerman. He thought Zimmerman was going to kill him.