NEW : They also accused the defense of trying to `` backdoor some very negative character evidence '' into the trial . Judge allows presentation of Trayvon Martin 's toxicology test that shows THC was in his system . Comment: Martin 's father , Tracy , testifies about hearing 911 call , says he could n't tell who it was screaming . Several defense witnesses testify it was George Zimmerman calling for help . Zimmerman is charged with second-degree murder for killing 17-year-old Martin .
NEW : Judge allows presentation of Trayvon Martin 's toxicology test that shows THC was in his system . Comment: Martin 's father , Tracy , testifies about hearing 911 call , says he could n't tell who it was screaming . Several defense witnesses testify it was George Zimmerman calling for help . Zimmerman is charged with second-degree murder for killing 17-year-old Martin .