Zimmerman didn't actually claim SYG - I think the story he eventually decided on was that he was pinned by Martin, meaning that he couldn't run away and SYG was irrelevant. It may have encouraged him to chase after Martin in the first place though.
There are different aspects to SYG.
Zimmerman didn't claim the immunity to prosecution offered under SYG. That would have involved a pre-trial hearing about his self defence claim at which time the case would have likely been dropped.
From the law in question;776.032 Immunity from criminal prosecution and civil action for justifiable use of force.—
(1) A person who uses force as permitted in s. 776.012, s. 776.013, or s. 776.031 is justified in using such force and is immune from criminal prosecution and civil action for the use of such force, unless the person against whom force was used is a law enforcement officer, as defined in s. 943.10(14), who was acting in the performance of his or her official duties and the officer identified himself or herself in accordance with any applicable law or the person using force knew or reasonably should have known that the person was a law enforcement officer. As used in this subsection, the term “criminal prosecution” includes arresting, detaining in custody, and charging or prosecuting the defendant.
(2) A law enforcement agency may use standard procedures for investigating the use of force as described in subsection (1), but the agency may not arrest the person for using force unless it determines that there is probable cause that the force that was used was unlawful.
(3) The court shall award reasonable attorney’s fees, court costs, compensation for loss of income, and all expenses incurred by the defendant in defense of any civil action brought by a plaintiff if the court finds that the defendant is immune from prosecution as provided in subsection (1).
This is the law that meant Zimmerman wasn't immediately arrested for shooting Martin. It offers such complete immunity that even arresting someone who has definitely shot and killed another person is a huge financial risk for the police department and state in general. Zimmerman didn't claim this, which is a good thing, but...
There are other aspects to the law. Again, looking at the
jury instructions there is this part;
In deciding whether George Zimmerman was justified in the use of deadly force, you must judge him by the circumstances by which he was surrounded at the time the force was used. The danger facing George Zimmerman need not have been actual; however, to justify the use of deadly force, the appearance of danger must have been so real that a reasonably cautious and prudent person under the same circumstances would have believed that the danger could be avoided only through the use of that force. Based upon appearances, George Zimmerman must have actually believed that the danger was real.
If George Zimmerman was not engaged in an unlawful activity and was attacked in anyplace where he had a right to be, he had no duty to retreat and had the right to stand his ground and meet force with force, including deadly force if he reasonably believed that it was necessary to do so to prevent death or great bodily harm to himself or another or to prevent the commission of a forcible felony.
In considering the issue of self-defense, you may take into account the relative physicalabilities and capacities of George Zimmerman and Trayvon Martin.
If in your consideration of the issue of self-defense you have a reasonable doubt on the question of whether George Zimmerman was justified in the use of deadly force, you should find George Zimmerman not guilty.
Italics are explicitly from the SYG legislation. But also notice how the burden of proof rests on the state here.
Self-defence is traditionally an affirmative defence. That is, the defendant has to actively prove - beyond reasonable doubt - that they were acting in self defence.
Under SYG and the related Floridian self-defence laws this is flipped. In this case the state had to prove, beyond reasonable doubt, that Zimmerman
wasn't acting in self defence. Or rather, that he didn't believe himself to be acting in self defence. That's one hell of a barrier to conviction of anyone with any sort of self-defence claim.
Combine this hurdle with the immunity and financial threats to the police department for prosecuting self-defence cases and you have a disincentive to prosecute these sorts of hard cases, which are the very ones that need resources and effort poured into to try to resolve.
Pile on top of that racial inequalities within the justice system and you can easily get the impression that these laws are a legal license to
shoot black people and get away with it.