Trayvon Martin was shot and killed by a neighborhood watch coordinator named George Zimmerman on February 26, 2012. Trayvon was an unarmed, 17-year old African-American boy. So far, no charges have been filed against George Zimmerman because he claims he was acting in self defense.
Florida has a unique self defense law called a "Stand Your Ground" law. The Florida law, in contrast to other more traditional self-defense laws, states that "a person does not have a duty to retreat" before using deadly force in self defense.
Utah's self defense law similarly states that "A person does not have a duty to retreat from the force or threatened force . . . in a place where that person has lawfully entered or remained."
But procedure is everything in criminal law. The police have to follow certain procedures in collecting evidence. The prosecuting attorney has to jump through procedural hoops before going to trial, and the trial judge has to carefully follow procedure to avoid being overruled on appeal. The definition of self defense is not what is preventing an arrest and prosecution in the Travon Martin case. The procedure that police have to follow is the stumbling block.
The difference between Florida's law and Utah's is that under Florida law police have to show probable cause that the shooter did not act in self defense. And they have to show it before they can make an arrest or file charges. Specifically, it says that a police agency "may not arrest [a] person for using force unless it determines that there is probable cause that the force that was used was unlawful." This adds an extra step to what the police need to prove before they can go forward with a charge and arrest.
To add teeth the Florida law makes police put their money where their mouth is. If police cannot prove probable cause, they will have to pay the defendant's attorney fees, court costs, loss of income, and "all expenses incurred." So if police arrest too early and can't disprove self defense basically at the time of arrest, they can end up paying huge lawyers' bills. Prosecutors and police hate this so much they are asking the Florida legislature to repeal the stand-your-ground law.
In Utah, self defense is an affirmative defense. The police and prosecution do not have to do anything to disprove affirmative defenses before trial. At trial, if there is any evidence of self defense, then the prosecution has the burden of disproving it. But in a case like Trayvon Martin's, it might be difficult for the defense attorneys to show any evidence of self defense without their client testifying about what happened. That can be risky and most criminal defense lawyers would love the option to have their client remain silent depending on what the evidence shows.
The Florida law adds an additional hurdle to what the police have to be able to prove before they can arrest someone. That is good for criminal defendants because it means that they are less likely to be arrested as part of a preliminary investigation. Prosecutors and police always have final say over who they arrest and who they prosecute. But the hurdle that is most likely causing police to wait to charge Trayvon Martin's killer is not part of the law in Utah.