LAW PROFESSOR: Here's How I Would Have Prosecuted George Zimmerman

Reuters/Joe Burbank

Assistant state attorney John Guy responds to defense attorney Don West (R) after an exchange of words following a late night hearing in the George Zimmerman trial in Seminole circuit court, in Sanford, Florida, July 9, 2013.

George Zimmerman's prosecutors had a very difficult task before them, but one law professor says they still could have made a stronger case.

"What you need in a criminal case is you have to lay out a theory of why you believe this crime was committed and you have to stick with the theory and you have to explain the theory," University of Florida law professor Kenneth Nunn tells us.

During closing arguments, prosecutors focused largely on inconsistencies and supposed exaggerations in Zimmerman's recounting of the night he killed 17-year-old Trayvon Martin, including his assertion that the teen grabbed for his gun despite the lack of DNA evidence.

But these arguments simply cast some doubt on Zimmerman's story instead of proving the prosecution's case, Nunn told us after the "not guilty" verdict.

Casting doubt on a witness's story is "great if you're a defense lawyer and not enough if you're a prosecutor," Nunn said. Of course, it's the prosecutor's job to prove guilt beyond a reasonable doubt.

To meet that high burden, Nunn said he would have stuck to the facts supporting Zimmerman's guilt including his pursuit of Martin against a 911 operator's advice and his decision to leave his car with a gun that was ready to fire. Nunn believes there was enough evidence to convict Zimmerman of at least the lesser charge of manslaughter.

Not everybody shares that belief. The Trayvon Martin case is "very, very sad," but the prosecution simply didn't have enough evidence to refute Zimmerman's self-defense claim that he feared for his life, law professor Kevin Brown tells us. Prosecutors have a very high burden of proof.

"The jury didn't find Zimmerman innocent," Brown said. "They found him not guilty."