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Crane operator allegedly had pot, prescription drugs in blood

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(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 Salvation Army 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.

The mayor pushed a new set of demolition standards and controls, promising he'll pursue whatever action is needed "in order to better ensure our collective public safety."

He also promised answers.

"I commit to you that we will make every effort ... to find out what went wrong," Nutter said.

Witnesses described an ominous rumble before the building came down, spurring panic on the streets.

"You felt it shake," Jordan McLaughlin told CNN affiliate KYW. "There (were) people that actually fell over. People started screaming, they ran across the street. There was people inside the building, you heard them scream."

Searchers climbed over shards of wood, concrete and rebar looking for survivors, like the 61-year-old woman pulled alive from the rubble early Thursday. This search was called off late Thursday afternoon, by which time prosecutors and city officials had toured the scene.