The envelope, which had swastikas on it, was filled with a white powdery substance, forcing the Departamento de Policía de Los Ángeles, LADF Hazmat and the bomb squad to respond.
The group from Recall Gascon’s Los Angeles headquarters was also being tested to make sure they hadn’t been exposed to anything hazardous. Authorities later determined the substance to be baking soda.
The group told FOX 11 Los Angeles they receive a lot of hate mail at their office.
Gascon has been criticized in L.A. for his progressive policies that some claim are too lenient on offenders and protect criminals over victims.
His policies were most recently in the spotlight earlier this month when two El Monte police officers were killed by a man who was on probation after receiving a lenient sentencing due to a plea deal over a gun offense.
Fox News’ Bill Melugin contributed to this report.