Defence attorney explains how lack of forensic evidence would complicate potential prosecution of George Zimmerman

Florida prosecutors face significant hurdles building a case against the man who killed Trayvon Martin, a legal expert has told the Guardian.

Jonathan Turley, a professor at George Washington University and a defence attorney, said the case had several "murky" elements which are likely to prove difficult for the prosecution, including within the 911 tape which appears to suggest Zimmerman was the one in pursuit of Martin.