A jury found Griffin Campbell guilty of involuntary manslaughter, reckless endangerment, causing a catastrophe and aggravated assault for his role in the June 2013 collapse, which sent a four-story wall crashing down onto a neighboring thrift store
He is scheduled to be sentenced in January.
Campbell's demolition plan left a four-story masonry wall unsupported at the site, the Philadelphia District Attorney's Office said in a statement.
Prosecutors charged him with third-degree murder
later that year. But jurors acquitted him of those more serious charges Monday.
"No verdict can replace the lives that were lost on that June morning," Philadelphia District Attorney R. Seth Williams said in a statement
, "but I hope today's verdict brings more closure and healing to the friends and families of those who were injured and lost their lives."
Attorney William Hobson, who represents Campbell, said he planned to ask a judge to overturn the aggravated assault conviction, arguing that it was inconsistent with the jury's other findings.
The case, Hobson argued, showed that the city's loose regulation of building demolitions at the time of the collapse also played a role in the disaster.
"The real tragedy to this case was avoidable in so many ways," he said.
Prosecutors: Profit was aim in demolition method
Prosecutors had argued
that Campbell chose to maximize profits rather than demolishing the building the right way.
A day before the collapse, Campbell removed bricks and braces that had supported the wall, even though an architect warned him not to, prosecutors alleged.
Campbell promised to build scaffolding to support the wall and said he would reduce its height to the roofline of the Salvation Army building, the District Attorney's Office said.
"In reality, however," prosecutors said, "Campbell was unwilling to pay for enough labor to perform the task."
Collapse left store customers trapped in rubble
The building Campbell was working on collapsed onto the Salvation Army Thrift Store next door with an ominous rumble, witnesses said at the time.
Customers and employees were trapped inside under a tangled pile of wood, concrete and rebar.
Six people were killed and more than a dozen others were injured.
In July, excavator operator Sean Benschop pleaded guilty to six counts of involuntary manslaughter and other charges in the case
. He's set to be sentenced later this week and could face up to 20 years in prison.