Story highlights Lawyer says his client, the crane operator, "was not responsible"

6 died, 13 were injured when a building being torn down collapsed on a thrift store

A law enforcement source had said marijuana was found in the crane operator's blood

Mayor says the man arrested, property owners bear "ultimate ... responsibility"

The 42-year-old crane operator wanted on involuntary manslaughter and other charges tied to a deadly Philadelphia building collapse turned himself in Saturday, a police spokesman said.

Sean Benschop will be charged with six counts of involuntary manslaughter, 13 counts of recklessly endangering another person and one count of "risking a catastrophe," officials said.

Wednesday's building collapse in downtown Philadelphia left six dead and 13 people injured.

Blaming the suspect's "reckless and irresponsible behavior" for the casualties, Philadelphia Mayor Michael Nutter said Saturday that he hopes Benschop faces "the harshest level of charges ... and he is punished accordingly."

"Justice will only be served if Sean Benschop receives a sentence that buries him in a jailhouse forever, just like his victims were buried on Wednesday," the mayor said.

Daine Grey, Benschop's attorney, told reporters Saturday that while his client feels "extremely sympathetic and remorseful," he's not guilty of any crime.

"This was an accident, but Mr. Benschop was not responsible," Grey said, in remarks captured by CNN affiliate WPVI . "And we believe that, in time, the facts will show that he is not responsible."

A judge signed an arrest warrant -- which had been approved by Philadelphia District Attorney Seth Williams -- on Friday night or Saturday morning, police said.

Benschop should make his first court appearance via closed circuit TV within 12 to 24 hours of his arrest, according to Philadelphia police spokesman Lt. John Stanford. At that point, a judge will determine what the bail amount will be in his case.

"The district attorney hopes the arrest of the defendant will be of some comfort to all of the victims and their families affected by this heartbreaking tragedy," district attorney's office spokeswoman Tasha Jamerson said.

Benschop allegedly was working a crane to tear down a vacant building in downtown Philadelphia when a four-story wall collapsed onto a Salvation Army thrift store, causing an ominous rumble followed by 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.

JUST WATCHED Woman pulled from rubble after 12 hours Replay More Videos ... MUST WATCH Woman pulled from rubble after 12 hours 02:58

Benschop, the crane operator, had marijuana and pain medication in his blood after the collapse, a law enforcement source told CNN.

Pennsylvania court records indicate Benschop, who also went by the alias Kary Roberts, has been arrested multiple times in the past two decades. Many of the related charges -- related to alleged firearms violations and theft -- were withdrawn, dismissed or resulted in not guilty verdicts, though he was found guilty in the mid-1990s on drug charges.

A day after publicly apologizing "to the victims and their families" and promising to do everything possible "to find out what went wrong," Nutter pressed Saturday to get answers from two property owners who hired Benschop to operate heavy machinery.

"These three individuals bear the ultimate and sole responsibility for this tragedy," the mayor said.