In the dark hours that followed, the finger-pointing began.
Neighbors blamed the city and the Department of Licenses & Inspection for not sealing the former factory, which attracted squatters and drug addicts, despite numerous complaints.
City officials insisted that they've spent months chasing the New York-based developers who own the building, and were on the verge of taking them to court for violating city codes and for not paying property taxes.
Now, officials said, they'll focus on trying to pursue criminal-negligence charges against the owners, Michael and Yechiel Lichtenstein, of York Street Property Development LP.
For their part, the Lichtensteins lawyered up and issued a statement expressing their sorrow over the tragedy and their willingness to cooperate with the upcoming investigation.
In coming days, the city will lay its fallen heroes to rest.
But the finger-pointing and the anger will linger, like the smoke hovering over the smoldering rubble.
East Kensington resident Chris Sawyer said he began worrying about the vacant factory building last fall.
"Before winter set in," he said, "I thought we might have homeless junkies run in there, start a fire to stay warm, then shoot up heroin and not be cognizant as it got out of control."
After gathering information about the property - including looking at Google satellite photos of the building that appeared to show part of the roof collapsing - Sawyer rounded up some neighbors to bombard the city's 3-1-1 service with calls.
"We were told that L&I wasn't going to do anything because it would've cost them $20,000 to reseal the building," Sawyer said. "This all could have been prevented if they had just sealed the perimeter."
"We're going through this over and over again, the same script," said Jeff Carpineta, president of the East Kensington Neighborhood Association.
An abandoned furniture-manufacturing plant at Front and Master streets was destroyed by a six-alarm fire in 2008.
"This is what's going to continue to happen unless the city comes up with a different response," Carpineta said. "What's horrific this time is that lives were lost. Families were destroyed."
City officials insisted that they took concerns about the Buck building seriously after fielding nine complaint calls from residents in November.
L&I followed its three-strikes-and-you're-out approach to dealing with the Lichtensteins, who bought the Buck building in 2009 and acquired a zoning permit to transform it into a mixed-use property with dozens of apartments.
An inspector visited the site in November, and the owners were sent a violation notice for failing to maintain the property, said L&I Commissioner Fran Burns.
A follow-up visit in December resulted in another violation notice, and the same happened in January, she said. A fourth violation was sent last month.
The agency was in the process of preparing for a court date over the violations, all of which were ignored by the Lichtensteins, who own 34 other properties in the city, according to Everett Gillison, Mayor Nutter's chief of staff.
The city also was pursuing the Lichtensteins for $59,498 in unpaid real-estate taxes that they owed on the building. Revenue Department records show that the building has had three liens placed against it. (The developers also owe $278,610 in back taxes on a property they own at 728 Market St.)
Gillison said the city was in the process of having the East Kensington factory building listed for a sheriff sale in June or July. And simply sealing the building as neighbors suggested would have required a court order, Burns said.
"You can see the city of Philadelphia uses every means we have to bring owners into compliance," he said.
Gillison stressed the importance of the city following its own rules for dealing with property owners, but noted the need for a stronger message to be sent in light of Monday's tragedy.
He said the city would work with the District Attorney's Office to see if criminal-negligence charges could be brought against the Lichtensteins.
All of the talk likely meant little to the families of David Sweeney and Robert Neary, who perished in the blaze, and their fellow firefighters, Francis Chaney and Pat Nally, who were rescued from the rubble of the furniture store.
Fire Commissioner Lloyd Ayers said the fire started inside the Buck building at 3:13 a.m. and reached five alarms in less than an hour. It was brought under control at 5:21 a.m., but the tragedy struck soon after.
"This is a dark day," said city Managing Director Richard Negrin. "We lost two of our heroes."
- Daily News staff writer
Morgan Zalot contributed
to this report.
Contact David Gambacorta at 215-854-5994 or gambacd@ phillynews.com, or follow on Twitter @dgambacorta.