Fireworks have often been used by terrorists to power their bombs, including by the man who tried but failed to detonate a car bomb in Times Square. He bought fireworks from a different Phantom Fireworks store, in Pennsylvania.
"Fireworks will give you what you need in terms of blast," said Kevin Barry, retired detective first grade, NYPD Bomb Squad.
Barry told ABC News that while the ingredients are easily purchased -- the actual assembly instructions are still hard to find and follow.
"What it seems they did was purchased commercially manufactured mortars, ripped them down and ripped out the powder," he said. "When you confine this powder in a pressure cooker it is very powerful."
The charging document filed in the case against 19-year-old Dzhokhar Tsarnaev also notes that FBI agents found "a large pyrotechnic" in his college dorm room.
Federal agents have analyzed the two pressure cooker bombs used in the Boston Marathon attack and confirmed early speculation that the other components were also built largely, if not entirely of commercially available items, including parts of a remote control toy car, BBs and small nails.
The analysis was circulated to law enforcement agencies Tuesday evening in a federal law enforcement joint intelligence bulletin.
The report notes that a similar device was found in the thwarted 2010 attempt to set off explosives in Times Square.
"Terrorists can exploit the innocuous appearance and transportability of pressure cookers to conceal IED components," the bulletin says.