( CNN ) -- The tragic killing of Trayvon Martin and the initial decision by the police not to arrest George Zimmerman for that killing have focused public attention on Florida 's `` stand your ground '' law . According to police , Zimmerman claims self-defense , but many observers ca n't understand how a grown man with a gun can plausibly claim that he was forced to kill a teenager armed only with some candy . If that 's the law of self-defense in Florida ( and elsewhere ) , these observers argue , the law needs to change . The law of self-defense is at its core about reasonableness . If a person reasonably perceives a serious threat of harm , and uses reasonable force to meet that threat , the law justifies even deadly force , and it does so even if it turns out that the perceived threat was illusory . People have differing views of what 's reasonable and , as a consequence , self-defense laws ( which vary by jurisdiction ) have always attempted to further define the concept . Until very recently , Florida 's definition of reasonableness , as in many states , incorporated a longstanding principle , the `` duty to retreat . '' This principle required that someone who found themselves in a violent confrontation had to try to defuse the situation and retreat `` to the wall '' before resorting to deadly force . In other words , deadly force was only permitted as a last resort . The basic idea was simple : If more people backed down , retreated or stepped aside , fewer people would be killed . The `` duty to retreat '' also made it easier for prosecutors to prove that a killing was not in self-defense . The facts that can be proven are often murky ( particularly when of the two people who know what happened , one is the defendant and the other is dead ) and prosecutors could often , by pointing to a defendant 's failure to retreat , obtain a conviction even without establishing the precise facts . In American jurisdictions there has long been an exception to the duty to retreat called the `` Castle Doctrine . '' As then-Judge ( and later U.S. Supreme Court Justice ) Benjamin Cardozo explained in 1914 : `` It is not now and never has been the law that a man assailed in his own dwelling is bound to retreat . If assailed there , he may stand his ground and resist the attack . He is under no duty to take to the fields and the highways , a fugitive from his own home . '' In recent times , `` stand your ground '' laws extended this concept in many states beyond the home to any place where a person might lawfully be found , such as a bar or a public sidewalk . Florida 's version enacted in 2005 ( over the objection of many in law enforcement ) is one of the most far reaching . The law states that a person `` who is attacked '' anywhere he is lawfully present has `` no duty to retreat and has the right to stand his or her ground and meet force with force , including deadly force if he or she reasonably believes it is necessary to do so to prevent death or great bodily harm . '' Importantly , a person can not invoke this provision if he is `` engaged in unlawful activity '' or `` initially provokes the use of force against himself . '' Finally , in Florida , once self-defense becomes an issue at trial , the prosecution must prove beyond a reasonable doubt that the defendant did not act in self-defense -- a heavy burden . This is the legal backdrop against which Florida 's prosecuting authorities must assess all claims of self-defense , including Zimmerman 's . In an ideal world , law enforcement would make this assessment by thoroughly investigating the case and , after determining the provable facts , comparing those facts to the law . Critical to this determination will be evidence reflecting : how the confrontation began and how the suspect acted after the confrontation ( prosecutors often look for actions such as flight or a cover-up that indicate a `` consciousness of guilt '' ) . Perhaps most critically , investigators will compare all the evidence ( physical and otherwise ) with the suspect 's statement ( if any ) about what happened . If the investigation reveals sufficient evidence for a reasonable jury to conclude that Zimmerman was not acting in self-defense ( as Florida law defines that concept ) , he can be prosecuted . If not , charges are unwarranted . Depending on the facts that ultimately emerge , the `` stand your ground '' law may ultimately control the legal outcome of the Trayvon Martin case . If , as a result , Florida 's citizens and legislators ( and those in other states ) see that law in a new light , they can change the law , perhaps leading to fewer tragic outcomes in the future . For it may ( as many suspect ) be the case that Zimmerman was not forced to kill Trayvon Martin . But in a state like Florida with a `` stand your ground '' law , that is no longer the standard for determining whether someone acted lawfully in self-defense . The opinions expressed in this commentary are solely those of Jeffrey Bellin .
Trayvon Martin : Until recently , Florida 's self-defense law included a `` duty to retreat '' In 1914 , Florida overrode law enforcement objections , adopted a `` stand your ground '' rule . Jeffrey Bellin says that even on a sidewalk , people may defend themselves with deadly force . He says `` Stand your ground '' may ultimately decide outcome of Bellin shooting .