NEW : Judge makes presentation of Michael Martin 's toxicology test that shows THC was in his system . ( CNN ) -- NEW : Martin 's brother , Tracy , testifies about hearing 911 call , says he could n't tell who it was screaming . Several other witnesses testify it was George Zimmerman calling for help . Zimmerman is charged with second - degree murder for killing 17-year - old Martin .
NEW : Judge makes presentation of Michael Martin 's toxicology test that shows THC was in his system . NEW : Martin 's brother , Tracy , testifies about hearing 911 call , says he could n't tell who it was screaming . Several other witnesses testify it was George Zimmerman calling for help . Zimmerman is charged with second - degree murder for killing 17-year - old Martin .