Thirteen others were buried in rubble but survived when a towering wall from an adjacent demolition project collapsed onto the small store at 22nd and Market streets in Center City in 2013. Some suffered permanent injuries.
Two unqualified demolition contractors are serving long prison terms, but the building owner and the architect who oversaw the demolition were never charged.
The civil trial has stretched over five months before Tuesday's verdict. The jury in less than a day found all defendants liable and will return Friday to consider damages.
The defendants include the owner of the building being demolished, Richard Basciano; architect Plato Marinakos Jr.; the Salvation Army; and the imprisoned contractors.
Two powerhouse Philadelphia lawyers squared off in court for closing arguments last week - 91-year-old Richard Sprague for Basciano and disaster attorney Robert Mongeluzzi for several plaintiffs.
Basciano, also 91, was hoping to redevelop a block of seedy properties he had held for 20 years. His architect, Plato Marinakos Jr., who oversaw the demolition, received immunity from prosecutors for his cooperation.
Mongeluzzi argued that they hired cut-rate workers to raze the downtown building despite the risk to the public. The workers took the four-story building down from the inside out, destabilizing the brick exterior walls.
He faulted the Salvation Army for keeping the store open despite warnings about the demolition. A lawyer for the Salvation Army called the charity blameless.
The catastrophe led the city to tighten its requirements for getting demolition permits. A city inspector killed himself days after the collapse, although no evidence surfaced that he did anything wrong.
Campbell was being paid $112,000 for the job, a fraction of the other bids. He had no comparable experience. Campbell is serving a 15- to 30-year sentence for involuntary manslaughter and other offenses. Sean Benschop, who was operating the machine despite taking Percocet and marijuana for medical problems, was sentenced to 7 to 15 years in prison for similar crimes.
The victims included the 24-year-old daughter of the city treasurer, who died along with a friend as they dropped off donations.