( 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 . CNN 's Greg Botelho and Phil Gast contributed to this report .
13 died , 6 were injured when a building collapsed in marijuana . Walls fell on a City Hall thrift store , pinning people in the rubble . The building was being torn down at the time . A Salvation Army source says marijuana , pain medication were in crane operator 's blood .