Florida's increasingly controversial "stand your ground" law was passed in 2005, eliminating the requirement that a person seek an alternative -- like fleeing -- before using force if they felt they were in physical danger.
The National Rifle Association and other advocates had argued that citizens were being arrested for merely defending themselves.
Florida, like many other states, has long held that citizens have the right to defend themselves in their own homes. Court rulings have expanded that right to include employees in workplaces and drivers in their cars. But there was long a reluctance to extend those rights to public places, so judges had ruled that citizens under threat must make some alternative attempt to violence to escape danger.
In 2005, the Florida House of Representatives voted 94-20 in favor of a new, "stand your ground" bill that eliminated the requirement to flee.
The state Senate passed the bill 39-0, and Governor Jeb Bush signed it into law.
Martin was returning to a friend's home in the gated Florida community of Sanford on Feb. 26, where Zimmerman was acting as a neighborhood watchman when Zimmerman spotted him and called police, describing the teen as suspicious.
He began to follow Martin, and continued speaking with police, who warned him repeatedly not to approach Martin.
Martin, meanwhile, was on the phone with a 16-year-old female friend, who told ABC News that she urged Martin to run.
She said she heard some pushing, and then the line went dead.
"He said this man was watching him, so he put his hoodie on. He said he lost the man," the girl told ABC News. "I asked Trayvon to run, and he said he was going to walk fast. I told him to run but he said he was not going to run."
Zimmerman was reportedly charged with assault on a police officer in 2005, when he was 21, after a scuffle with police over the arrest of one of his friends for underage drinking in a local bar. He accepted a pre-trial diversion that kept him from being convicted of a felony -- an outcome that might have prevented him from receiving a permit to carry a gun.
Sonner said he couldn't predict whether charges would eventually be filed against Zimmerman, but he is prepared for anything.
"It's going to the grand jury on April 10, and then the grand jury will make that decision at that time,'' Sonner said.
"So they can file charges at any time -- tomorrow is Monday -- they can file tomorrow," he said. "Whether they will or not? Thus far they have not, and it is my contention, when all the evidence I believe is going to come forward, I think it clearly going to be a case of self-defense."