A grand jury will look into last week's building collapse in Center City, District Attorney Seth Williams said today.

The collapse at 22nd and Market Streets on Wednesday killed six people and injured 13 when a four-story building that was being demolished toppled onto an adjoining Salvation Army thrift store.

Sean Benschop, the 42-year-old excavator operator facing involuntary manslaughter and other charges in connection to the incident, also suffered minor injuries.

"As of today, I will be convening an investigating grand jury to look into the deadly collapse," Williams said at a news conference.

He said the grand jury will hear from witnesses, gather documents and evaluate other information to "determine if anyone, other than Mr. Benschop, should be held criminally responsible."

The grand jury may look into municipal agencies or departments, policies and protocols, Williams said.

Though city agencies could be targets of the probe, the district attorney said an outside investigator wasn't necessary.

"There is no need for a special investigator," he said. "That is the role of the grand jury."

Several civil lawsuits have been filed over the incident, and lawyers and experts for the victims who filed suit were inspecting the site on Sunday. The Philadelphia City Council is also launching its own probe into the collapse.

Benschop, the excavator operator, was taken into custody Saturday and is being held without bail. He is charged with six counts of involuntary manslaughter, 13 counts of recklessly endangering another person and one count of risking catastrophe, police said. His next court hearing is scheduled for June 26.

Prosecutor Jennifer Selber said at today's news conference that Benschop was "under the influence of a controlled substance" at the time of the incident and "was too impaired to safely operate that crane."

Benschop may have also been using the machinery improperly, Selber said.

He worked for contractor Griffin Campbell's construction company, which property owner Richard Basciano had hired to demolish the building. A demolition permit says the contractor was being paid $10,000 for the job. Neither Campbell nor Basciano have been charged with any crimes.

Investigating grand juries determine if there is sufficient evidence for prosecutors to file charges in a case.

Williams asked for patience while the grand jury investigates.

"I know Philadelphians demand action," he said. But he added: "Our office will not be part of a rush to judgment."