Two leading U.S. lawyers have expressed scepticism over the second-degree murder charges against George Zimmerman, after the release of fresh evidence and eyewitness accounts.

Zimmerman, a 28-year-old neighborhood watch volunteer, shot Trayvon Martin (17) on February 26. He claims he acted in self defence.

Harvard law professor Alan Dershowitz told ABS News,"There is no second-degree murder evidence in this case".

Adding, "It's a very close case".

Over the past week, new details regarding the events of Feb. 26 have emerged including  photographs of the scrapes on Martin's knuckles, as well as Zimmerman's battered and swollen face.

Also eyewitness accounts back up Zimmerman’s story that he acted in self defence.

One eye witness told investigators he saw the deceased teenager on top of Zimmerman, assaulting him mixed martial arts-style.

"I'd rather play the defense than the prosecutor, because there's no way you get a murder-two conviction," journalist-attorney Geraldo Rivera told "The O'Reilly Factor" last week.

Special Prosecutor Angela Corey, the state attorney in Florida's Fourth Judicial Circuit Court, was assigned to the case almost a month after the shooting. Speaking last weekend, Corey said that not all evidence was in the public domain.

"What the general public has to remember and the media has to remember is that there is a lot we cannot release by law," Corey said.

Zimmerman’s Irish American attorney, Mark O’Mara agreed.

"[It is] way too early to tell," he said. "That's me not only commenting on evidence, but the weight of all the evidence. And I don't even have all the evidence."

Attorney Mark O’Mara and George ZimmermanGoogle Images