Crews still need to search about 20 percent of the site of the collapse, including the back of a thrift store onto which the vacant four-story building under demolition collapsed, an effort that was expected to last through the afternoon, authorities said.
At least 14 people were injured in Wednesday's collapse, including the 61-year-old woman who was pulled from the debris nearly 13 hours later and hospitalized in critical condition.
"That's why we stay the course," City Fire Commissioner Lloyd Ayers said. "This person being pulled out alive is what this rescue operation is all about."
The sense of urgency had subsided after workers combed through bricks and rubble using buckets and their bare hands well into the night. A crane arrived at the site Thursday morning to be used later in the search.
It was unclear what role the demolition work might have played in the collapse, but the accident raised questions about how closely the highly visible spot on Market Street, one of Philadelphia's signature boulevards, was being monitored, particularly amid word of the demolition contractor's many legal and financial troubles. Officials from the U.S. Department of Labor and Occupational Safety and Health Administration were at the scene.
For weeks, people working nearby had watched with growing concern as a crew took down the vacant four-story building next to a Salvation Army thrift store at the edge of downtown.
A roofer atop another building didn't think the operation looked safe. A pair of window washers across the street spotted an unbraced, 30-foot section of wall and predicted among themselves the whole building would simply fall down.
On Wednesday, that's what happened. The unstable shell of a building collapsed into a massive heap of bricks and splintered wood, taking part of the thrift store with it.
"Our thoughts and our prayers go out to those who lost their lives, and their families," Mayor Michael Nutter said at a late-night news conference at which he announced the death toll. "At the same time, we pray that those who survive will recover not only physically, but certainly mentally from the trauma of being in a building and it suddenly collapses."
Witnesses said they heard a loud rumbling sound immediately before the collapse.
"I was standing there looking out my window, watching the men at work on the building, and the next thing I know I heard something go kaboom," said Veronica Haynes, who was on the fifth floor of an apartment building across the street. "Then you saw the whole side of the wall fall down ... onto the other building."
Several other witnesses said they had questioned how the demolition workers were tackling the job.
Roofer Patrick Glynn said he had been watching workers take down the building over the past few weeks, and he said he suspected a collapse was inevitable because of the way they were going about it.
"For weeks they've been standing on the edge, knocking bricks off," he said. "You could just see it was ready to go at any time. I knew it was going to happen."
Steve Cramer, who has been working as a window washer across the street, said the demolition crew left 30 feet of a dividing wall up with no braces and it compromised the integrity of the building
"We've been calling it for the past week — it's going to fall, it's going to fall," his co-worker Dan Gillis said.
Officials said the demolition contractor was Griffin Campbell Construction in Philadelphia. Messages left for Campbell were not returned.
Records show that Campbell was charged in 2005 with dealing crack cocaine near a playground. The charges were dismissed after prosecutors misplaced evidence.
He pleaded guilty in an insurance fraud case in 2009, and was acquitted of aggravated assault and related offenses in 2007.
Campbell has also filed for bankruptcy protection twice since 2010. The first bankruptcy was dismissed because he didn't follow through on a repayment plan approved by the court. A second bankruptcy petition was filed in March.
There were no existing violations on the collapsed building, and Campbell had proper permits for the work being done, according to Carlton Williams, of the city's Department of Licenses and Inspections.
The city issued a demolition permit for the four-story structure on Feb. 1. Records show the property owner as STB Investments Corp., a company linked to prominent businessman and developer Richard Basciano, who has been best known as the owner of porn theaters in New York City and Philadelphia.
Messages left at the company's New York offices were not immediately returned.
The accident happened on the western edge of downtown, between the city's business district and its main train terminal, 30th Street Station. The block had long been a seedy link between gleaming skyscrapers and the busy area around the station.
The collapse involved an empty building that once housed a first-floor sandwich shop and apartments above. The thrift shop was on one side. The other side was an adult bookstore and theater that had been taken down within the last few months.
A demolition expert wondered what precautions were taken to protect the Salvation Army store, especially since it remained open. Stephen Estrin, a Florida contractor who has testified as an expert at several trials involving building collapses, also questioned whether the demolition was being done by hand or with machinery. A piece of equipment with a claw device was seen amid the debris Wednesday.
"This is an inner-city demolition of a masonry building, which would normally be done manually because of the inherent risk — predictable if certain things are not done very slowly and very carefully — of a collapse," Estrin said. "One of the problems with claw work is it sets up a vibration in the walls."
Records show the collapsed building was sold to STB in 1994 for $385,894. Plans tentatively called for the block to be redeveloped into retail stores and apartments.
Rubinkam reported from northeastern Pennsylvania. Associated Press writers Ron Todt and Maryclaire Dale also contributed to this story.
Copyright 2013 The Associated Press.