“I’d be very, very surprised if we took it,” said one federal civil rights prosecutor, speaking anonymously because no decision had been made. “It’s a very tough, tough case to sell” because of the lack of witnesses.

“The difficult element would be proving racial motivation beyond a reasonable doubt,” said University of Michigan law professor Samuel Bagenstos, a former civil rights attorney in the Obama administration. “In most of these [hate crime] cases, you have someone who had made racial statements or you have a group who goes looking to attack a person based on their race.”

But in the confrontation between Zimmerman and Martin, “no one else was there who could testify about the motivation,” he said…

“Unless there is significant new evidence, I’d say it would be unlikely the department would bring a hate crimes charge,” Bagenstos said. “It would be very difficult to win, and they don’t bring charges they don’t think they can prove.”