(CNN) — Police are trying to track down a crane operator tied to a deadly building collapse this week in Philadelphia, issuing an arrest warrant for him on involuntary manslaughter and other charges, a law enforcement source with knowledge of the investigation told CNN.
Another source identified the wanted man as Sean Benschop, 42.
A four-story wall of a vacant building that was being torn down Wednesday collapsed onto a Salvation Army thrift store in downtown Philadelphia
Six people died and 13 were injured in the incident, which precipitated an extensive and exhaustive search for survivors.
In addition to involuntary manslaughter, the arrest warrant -- approved by Philadelphia District Attorney Seth Williams, according to the law enforcement source -- accuses the crane operator of causing a catastrophe.
A source at Philadelphia's City Hall with direct knowledge of the investigation told CNN on Friday that marijuana and pain medication were found in the crane operator's blood.
The district attorney's office did not return several calls Saturday from CNN seeking comment.
Witnesses described an ominous rumble before the building came down, spurring panic on the streets.
Afterward, searchers climbed over shards of wood, concrete and rebar looking for survivors, such as 61-year-old woman pulled alive from the rubble early Thursday.
The first lawsuit was filed that same day, by attorneys for a 54-year-old woman pulled from the rubble by a firefighter.
Mayor Michael Nutter publicly apologized Friday "to the victims and their families" and "to the survivors and their families" for the collapse.
He 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."
"I commit to you that we will make every effort ... to find out what went wrong," Nutter said.