The Bureau of Alcohol, Tobacco, Firearms and Explosives and the Citizens Crime Commission announced a $20,000 reward Thursday for information leading to the arrest and conviction of the person or persons responsible.
The fire destroyed the historic St. Leo The Great Roman Catholic Church on Keystone Street and Unruh Avenue.
"The case is still an ongoing criminal investigation, but our ATF fire investigators - who are certified in fire science - have made the determination it was arson," said ATF Special Agent Charles Doerrer. "We think there will be a lot of people who will come forward because this is sentimental to people in this neighborhood."
Former parishoners, including Francine Strick of Tacony, came by the church after hearing word that authorities believe the fire was intentional.
"There were lots of memories and a lot of love that went into that church. For someone to turn around and set fire to it, I can't imagine," said Strick.
Flames tore through the vacant property that was built in 1884. The blaze reached two alarms before it was brought under control.
St. Leo's merged with Our Lady of Consolation in 2013. The church closed in 2019 as a place of worship and was later added to the city's historic register. The church was sold a month ago to an owner who specializes in restoring churches and planned to rent it.
Authorities say the new owner is fully cooperating with the investigation.
Dozens of neighbors looked on as a contractor took a wrecking ball to the remains of the building on Monday, many of them saying goodbye to a church that has hosted generations of their families.
The fire left a freestanding wall facing Keystone Street, which the fire marshal said posed an imminent danger to the neighborhood and prevented investigators from getting inside to try and determine the fire's cause.
Anyone with information on the person or persons responsible for the fire should contact ATF at 1-888-ATF-TIPS (888-283-8477), email ATFTips@atf.gov, or contact ATF through its website at www.atf.gov/contact/atftips. Tips can also be made to the Philadelphia Fire Marshal's office via mobile device by following: bit.ly/PHLarsontips