Firefighters, assisted by search dogs, dug through piles of bricks into the night to extract survivors and recover bodies. After a grim evening in which the death toll climbed from one to six, rescuers celebrated briefly just before midnight when they extracted Myra Plekam, a 61-year-old Kensington woman who was taken to the Hospital of the University of Pennsylvania in critical condition.
Fire Commissioner Lloyd Ayers said 40 percent of the site still had not been searched Wednesday night and firefighters were proceeding slowly because of dangerous conditions.
City officials said they did not know how many people were in the store, on the sidewalk, or nearby at the time of the collapse.
"Our forces have been diligent. They have been determined and focused, and are some of the best in the country," Nutter said. "If anyone else is in that building, they will find them."
The rescue and clearance efforts were expected to continue into at least Thursday afternoon. Early Thursday morning, a crane was lifting debris into a dump truck that had just arrived at the scene. The work continued, with each filled dump truck leaving the scene and an empty one arriving.
Also in the early hours of Thursday, preparations were being made for a new shift of rescue workers to come on duty to replace the earlier crew. Although the debris was still being searched for anyone still trapped, one fire official at the scene said it was believed that all the missing were accounted for.
By 3 a.m., Battalion Chief Charles Lepre said that the basement had been searched with a telescope-like instrument and with a cadaver dog, but that no one was found there. And emergency workers used pokers to go through the first-floor rubble. He indicated that everyone who'd been reported to emergency officials had been found.
Witnesses said that, in recent days, they had watched with growing concern as the demolition progressed and the crews did not appear to properly support a wall that adjoined the thrift shop. One worker at the store had told her husband of large fissures in the wall.
Nutter declined to speculate about the cause of the 10:45 a.m. accident, saying the matter was under investigation. He said it was "not unusual" for a building to be occupied next to an ongoing demolition.
Carlton Williams, commissioner of licenses and inspections, said there were "no existing violations on the property. It was permitted, and the contractor did have a license."
Griffin T. Campbell, the contractor hired to demolish the cluster of decrepit commercial buildings, filed for bankruptcy protection in March. He has a criminal record stemming from a phony car-wreck scheme involving a Philadelphia police officer, according to court records.
Richard Basciano, the owner of the four-story building at 2136-38 Market, is best known as the colorful landlord of two now-closed adult movie houses in the neighborhood. He had announced ambitious plans to redo that section of Market.
Basciano could not be reached Wednesday, but Dean R. Phillips, a lawyer for Basciano's firm, said: "At this point, like everyone else, we are just trying to get our arms around this terrible tragedy and determine exactly what happened. Our hearts and prayers go out to the victims and their families."
Half the facade of the destroyed thrift shop was still standing Wednesday evening, with clothes hanging in the window.
Most of the injured escaped from the wreckage quickly, Nutter said. One woman, who was buried under debris for two hours, was able to walk out on her own, he said.
Law enforcement officials did not identify the victims, most of whom were taken to area hospitals; some were released later. But the wife of 68-year-old Liberian immigrant Borbor Davis of Upper Darby, a worker in the thrift shop, said authorities informed her that they had recovered her husband's body Wednesday evening.
"I'm not all right," said Maggie Davis, weeping softly when reached by phone. "He passed."
She gave the phone to her daughter, MaryAnne Mason, who was Borbor's stepdaughter.
"We're grieving," Mason said. "My mother is in a state of shock. She keeps saying: 'Oh, God, oh, God. My baby, my baby.' She hasn't stopped crying."
Ayers said most of the injuries appeared to be minor.
For much of the day, police halted traffic on Market from 20th to 30th Streets, triggering near-gridlock across much of western Center City.
Firefighters worked to clear away the news helicopters hovering over the scene because the noise was interfering with equipment being used to detect sound inside the wreckage.
Law enforcement sources said a crane operator was demolishing the four-story building - formerly home to a Hoagie City store - when he pulled out a second-story beam. The remaining structure toppled seconds later onto the two-story thrift shop.
Dee Lamar, an aide who works at the Sidney Hillman Apartments building near the site, was on the ninth floor when she heard a big explosion, she said.
"I looked out the window and the smoke and ashes everywhere," she said. "You couldn't see anything. When the smoke cleared, the building was gone."
More than a dozen roofers and painters were working on the nearby College of Physicians and Mutter Museum when they heard a sound "like a jet engine" and saw a plume of dust rising from the collapsing structures.
Workers and bystanders ran to the scene and immediately began pulling people from the wreckage. One man was unconscious on the sidewalk. A woman with a gash on her head and blood running down her neck staggered from the store, said Marc Newell, one of the first people on the scene.
Brian Mullins, 23, a painter at the College of Physicians, said he and others pulled six people out. "We saw the dust and we went running," he said.
"One of our maintenance people was trying to help get people out. . . . He could hear people screaming, 'Help me! Help me!' " said Quiana Brooks, a bookkeeper at Sidney Hillman.
Barbara Ruth, a resident in the 2100 block of Market, said that for days "there has been an enormous amount of noise" from the demolition, so the sound of the collapse was not that noticeable.
Jordan McLaughlin, 18, a student at Science Leadership Academy who was on his way to a dental appointment, said he watched in shock as the building collapsed. He dropped his book bag on the sidewalk and ran into the collapsed store.
"I have never seen anything like this," he said. "It was crazy."
Nadine White, the assistant manager of the shop, told her husband she had noticed huge cracks in the walls of the store.
"Everything was falling over," said White's husband, Kenneth Bond. "Everybody knew about it, but nobody said anything. They just kept working."
Bond, 56, of South Philadelphia, became alarmed Wednesday when he passed the store about 8 a.m. He called his wife.
"I had told her, 'Baby, this really doesn't look good,' " he said. "Somebody should have known something would happen."
White, 53, was trapped briefly in the collapse and rescued from the rubble by firefighters.
A local architect described the demolition work as "sketchy, at best."
"I actually saw it and said it doesn't look safe," said architect Joseph Sulvetta, whose office is nearby. He said it appeared that demolition crews had left a wall unsupported.
Campbell, 49, the contractor, could not be reached for comment.
According to court records, he filed for Chapter 13 bankruptcy protection in March, listing $221,000 in liabilities. In 2009, he pleaded guilty to having filed a false insurance claim in an auto collision that was actually a hoax.
Nutter's press secretary, Mark McDonald, said Campbell had met requirements for demolition contractors who are required to show proof of insurance and pay $300 for their permits. There are no criminal background checks and Campbell's conviction for insurance fraud was irrelevant, McDonald said.
Although the Department of Licenses and Inspections issues demolition permits, McDonald said it was up to a federal agency, the Occupational Safety and Health Administration, to oversee any safety issues at demolition sites.
An OSHA spokeswoman said the agency was investigating the accident.
Eight of the injured remained in hospitals Wednesday night.
At Thomas Jefferson University Hospital, two of the five people admitted with minor injuries were released. At Hahnemann University Hospital, one of three admitted remained in the hospital and was listed in fair condition.
At the Penn hospital, two patients were discharged and three held for observation, plus Plekam, the woman rescued just before midnight.
Contact Aubrey Whelan at 610-313-8112, firstname.lastname@example.org, or follow on Twitter at @aubreyjwhelan.