Daily Pakistan is reporting that a police constable pulled the pin from a grenade and caused it to explode in a Karachi courtroom after a judge asked him how it worked.

Daily Pakistan is reporting that a police constable pulled the pin from a grenade and caused it to explode in a Karachi courtroom after a judge asked him how it worked. 
The officer reportedly thought the weapon had been deactivated since that is the standard protocol for such devices presented as evidence, but this one was not.  
Five people including the officer and the judge are believed to have been injured from the blast which nearby authorities initially thought was the result of a terrorist attack.