Source: Crane operator had pot, prescription drugs in blood

(CNN) -- Marijuana and pain medication were found in the blood of the crane operator at the site of a deadly building collapse, a source at Philadelphia's City Hall with direct knowledge of the investigation told CNN on Friday.

Six people died and another 13 were injured when a four-story wall of a vacant building being demolished collapsed onto a thrift store in Philadelphia on Wednesday.

Mayor Michael Nutter publicly apologized earlier Friday "to the victims and their families" and "to the survivors and their families" for the collapse.

He spoke with reporters about a new set of demolition standards and controls that he wants to implement and vowed, "We will make every effort ... to find out what went wrong."