NEW YORK (AP) — New York police investigators say they’ve uncovered traces of substances common in explosives in a device that detonated when a Virginia man stepped on it in Central Park, resulting in the amputation of part of his leg.

Connor Golden, of Fairfax, Virginia, a college student at the University of Miami, was at the park July 3 with friends when he stepped on a rock covering the explosive and lost his lower left leg and foot.

Investigators don’t believe the device was meant to intentionally hurt anyone.

Police said Thursday the substances found in the investigation are legally available for sale in hardware stores and can be used with other products to develop homemade explosive devices. Investigators say they believe the explosive was made by someone experimenting with commercially available products.