Trayvon Martin, 17, was shot on February 26 in a gated community in central Florida by a neighbourhood watch captain, George Zimmerman, who later was released by police after claiming he acted in self-defence.
Benjamin Crump, the lawyer for Martin's family, said on Tuesday Martin had put on a hoodie after getting caught in the rain and was not aware he was being followed by Zimmerman.
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"He's just a kid trying to get home from the store and get out of the rain. That's it, nothing else," Crump told a news conference.
He said Martin's 16-year-old girlfriend was on the phone with him at the time and heard most of the altercation.
"What Zimmerman said is completely contradicted by the phone log," Crump added, urging authorities to arrest the neighbourhood watchman for killing Martin "in cold blood".
Speaking to ABC News, the girlfriend recalled that Martin "said this man was watching him, so he put his hoodie on. He said he lost the man".
"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," added the girlfriend, who was not identified.
The Justice Department said its Civil Rights Division plans to "conduct a thorough and independent review of all of the evidence".
The division examines cases in which discrimination on the basis of race, sex, disability, religion, and national origin are suspected.
The FBI is also investigating the racially charged killing.
Martin's case is heading to a grand jury, where a diverse group of citizens will decide whether to bring charges against Zimmerman, according to the local state attorney's office.
"I share in the desire of the family and the community to accurately collect and evaluate all the facts surrounding the tragic death of Trayvon Martin," Norman Wolfinger, state attorney for Brevard and Seminole counties, said in a statement.
