A new playground in South Philadelphia was set afire on June 17, melting plastic and charring fiberglass and metal. The playground, in FDR Park, had just been completed in October at a cost of $306,000.
City officials declared the playground a total loss.
Mayor Nutter called it "an act of evil."
A South Philadelphia man at the scene told investigators that he had spotted two unknown white males running from playground shortly before it erupted in flames, police said.
On Friday, police arrested that witness. Kevin Beattie, 26, of the 2400 block of South Camac Street, was taken into custody and charged with arson, risking a catastrophe, unsworn falsifying and other counts.