SANFORD, FL – JULY 8: The Father of Trayvon Martin, Tracy Martin, testifies as a defense witness in George Zimmerman trial in Seminole circuit court, July 8, 2013 in Sanford, Florida. Donnelly identified the screams as belonging to Zimmerman. Zimmerman has been charged with second-degree murder for the 2012 shooting death of Trayvon Martin. (Photo by Joe Burbank-Pool/Getty Images)