(CNN) -- A grand jury will investigate last week's deadly building collapse in Philadelphia to determine whether anyone besides a crane operator will face criminal charges in the case, Philadelphia District Attorney Seth Williams said Monday.
Williams' announcement came after authorities charged crane operator Sean Benschop with involuntary manslaughter and other counts, accusing him of being too impaired to operate a crane at the incident site.
A vacant building was being torn down in downtown Philadelphia when a four-story wall collapsed onto an adjacent Salvation Army thrift store on Wednesday, killing six people and injuring 13.
Williams, who said he would convene the grand jury Monday, added the panel will investigate "any and all aspects" of the collapse -- including city agencies and policies, "to determine if anyone in addition to Mr. Benschop should be held criminally responsible."
"I know Philadelphians demand action ... but our office will not be a part of a rush to judgment, so I ask and beg the patience of all Philadelphians as we work systematically, methodically and in accordance with the law ... to gather all the evidence," Williams told reporters at a news conference.
Benschop, 42, was arrested Saturday and charged with six counts of involuntary manslaughter, 13 counts of recklessly endangering another person, one count of causing a catastrophe and one count of risking a catastrophe, Williams said.
Toxicology results showed Benschop was under the influence of a controlled substance and was too impaired to operate the crane, Jennifer Selber, a Philadelphia assistant district attorney, said at the same news conference.
Earlier, a law enforcement source told CNN that Benschop had marijuana and pain medication in his blood after the collapse.
Other evidence indicates that Benschop was using the crane improperly, Selber said.
"It doesn't mean that other people aren't responsible as well. We just don't have the evidence at this point," she said.
Felicia Hill, 36, a mother of seven children, was employed as a sales associate at the Salvation Army and was working at the time of the collapse. "I'm going through a range of emotions," Hill said on Monday, "sadness, anger; right now I'm just distraught."
Hill said she feared she would die in the collapse, and that her children "wouldn't see their mother again." Hill was rescued by firemen and was hospitalized at Jefferson Hospital but released later that day.
Hill's attorney, Emmet Matten, announced plans to file a lawsuit but mentioned that Hill was "one of the lucky ones. There were six others who weren't so lucky."
On Saturday, Philadelphia Mayor Michael Nutter blamed Benschop's "reckless and irresponsible behavior" for the building collapse, but also said he was pressing for answers from two property owners who hired Benschop to operate heavy machinery.
Williams said he wouldn't speculate on who else might be charged. The grand jury, he said, will be able to issue subpoenas, interview witnesses and demand documents of various agencies.
Benschop, who maintains his innocence and is being held without bail, is next scheduled to appear in court on June 26.
Over the weekend, Benschop's attorney, Daine Grey, said his client "is being made the scapegoat in this situation."
"The victims here aren't just those who died and their families," Grey said. "My client is a victim as well. He's currently being looked at as the cause of everybody's pain, but that just isn't the case."
Grey told reporters Saturday that while his client feels "extremely sympathetic and remorseful," he is not guilty.
"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."
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 charges -- related to alleged firearms violations and theft -- were withdrawn, dismissed or resulted in not guilty verdicts. He was found guilty on drug charges in the mid-1990s.
CNN's Rande Iaboni, Susan Candiotti and Greg Botelho contributed to this report.