Police have released video showing fireworks that were launched next to a recycling plant on Cherry St that caught fire last week.
A hundred firefighters were called to the six-alarm blaze last Thursday at the Green For Life building.
Police now say that fireworks were seen being launched from an area next to the building just before the fire started.
The fireworks landed on the property.
Investigators are looking for a black pickup truck and a white sedan that were seen taking off.
They have released video of the fireworks.
Damage is estimated to be as high as $20 million.