Image copyright AP Image caption George Zimmerman has been arrested on assault charges since being cleared of murder in 2013

George Zimmerman will not face federal civil rights charges over the death of black teenager Trayvon Martin.

Attorney General Eric Holder said Martin's death was a "devastating tragedy" but the "high standard" for hate crime charges could not be met.

Mr Zimmerman shot and killed an unarmed Martin in Florida in 2012 but was found not guilty of murder at trial.

The case sparked a fierce debate about racial profiling and self-defence laws in the US.

Since the trial, Mr Zimmerman has been repeatedly in trouble with the law, arrested twice for assault. Both charges were dropped.

His lawyer Don West told the BBC he was relieved by the decision: "He was never able to relax completely until now."

Image copyright Reuters Image caption Trayvon's mother, Sybrina Fulton, has taken part in protests

Lawyers for the Florida man argued he had killed Trayvon Martin in self-defence after a confrontation.

But prosecutors said Mr Zimmerman, a neighbourhood watch volunteer, presumed Martin was suspicious, followed him with a gun and "wanted" to kill him.

Martin had been walking back from a convenience stores to a family member's house when he was killed.

"We, as a nation, must take concrete steps to ensure that such incidents do not occur in the future," Mr Holder said in a statement.

But he said the department's investigation did not show sufficient evidence that Mr Zimmerman wilfully deprived Trayvon Martin of his civil rights.