Lawyers who had been representing Zimmerman announced Tuesday that they were no longer handling his case because they hadn't heard from him since Sunday. They said he was suffering from high levels of stress.
U.S. Attorney General Eric Holder said Wednesday that he would act if evidence of a civil rights crime is found in the shooting.
Martin, 17, was shot and killed Feb. 26 by Zimmerman, 28, who reported to police that a suspicious man was walking through his Sanford community.
Although details of the incident remain murky, what is known is that Martin, who was African-American, ventured out from his father's fiancee's home to get a snack at a nearby convenience store. As he walked home with a bag of Skittles and an Arizona iced tea, he was shot and killed by Zimmerman, who is Hispanic.
Zimmerman claims the shooting was in self-defense after Martin attacked him and slammed his head against the sidewalk, according to police.
Martin's death has triggered a nationwide debate about race in America and Florida's "stand your ground" law, which allows people to use deadly force anywhere they feel a reasonable threat of death or serious injury.
On the night of the shooting, Sanford police questioned Zimmerman and released him without charges. Authorities said Zimmerman was not immediately charged because there were no grounds, at the outset, to disprove his account that he'd acted to protect himself.
Thousands have converged on Sanford to join in protests calling for Zimmerman's arrest and criticizing the police department's handling of the case.
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