The search for victims of a building collapse that killed six people wound down Thursday amid mounting questions about whether the demolition company that was tearing down the structure caused the tragedy by cutting corners.

The four-story building along Philadelphia’s busy Market Street collapsed Wednesday, trapping workers and others inside the Salvation Army thrift shop next door. Two employees were killed, a 35-year-old woman working her first day at the store and a 68-year-old Liberian immigrant. Lt. Col. Timothy Raines said the agency is “deeply saddened by the tragic loss of life.”

“Buildings get demolished all the time in the city of Philadelphia with active buildings right next to them. … They’re done safely in this city all the time,” Mayor Michael Nutter said. “Something obviously went wrong here yesterday and possibly in the days leading up to it. That’s what the investigation is for.”

Despite Nutter’s reassurances, Philadelphia began inspecting hundreds of demolition sites in the wake of the collapse. The Department of Licenses and Inspections said it had 300 open demolition permits throughout the city; inspectors had visited about 30 of the sites by Thursday afternoon and planned to get to the rest by next week.

The spot inspections included all four construction and demolition sites connected to Griffin Campbell Construction, the demolition contractor involved in Wednesday’s deadly collapse. The city found violations at two sites and ordered a halt to the work.

As details of Campbell’s checkered legal and financial past came to light, a city councilman charged that dangerous, under-the-radar tear-downs are taking place throughout the city and demanded a stricter application and inspection process for demolition companies.

More than 24 hours after the collapse, the search for the dead and injured was nearly complete, with no one else believed to be in the rubble. Firefighters hosed down piles of bricks to reduce the dust, and heavy machinery scooped up debris.

Rescue efforts were buoyed early Thursday when a woman was pulled out alive and conscious after 13 hours under the rubble. Nyra Plekam was hospitalized in critical condition and was said to be floating in and out of consciousness. At least 12 others were hurt, many with minor injuries, and five remained hospitalized.

“That’s why we stay the course,” fire Commissioner Lloyd Ayers said. “This person being pulled out alive is what this rescue operation is all about.”

Officials from the U.S. Department of Labor and Occupational Safety and Health Administration were at the scene.

The mayor said he was unaware of any complaints about the demolition work done by Campbell in the days before the tragedy. But OSHA said it had gotten a complaint May 15 that workers at the site were at risk of falling. The complaint was still open at the time of the disaster, U.S. Labor Department spokeswoman Leni Uddyback-Fortson said.

OSHA regulates the demolition industry and enforces standards meant to ensure worker safety. Among other things, its regulations forbid any wall section exceeding one story to stand alone without bracing, unless the wall was designed that way. Witnesses have said they saw a 30-foot section of unbraced wall before the collapse.

Also, a video of the demolition taken Sunday and posted on YouTube showed bricks raining down on the sidewalk as a worker used a backhoe and claw to remove a second-story front wall.

The sidewalk and the staircase leading up from a subway stop appeared open to pedestrians despite the falling bricks. Cars and trucks could also be seen going past, just a few feet away.