Kevin Golden was in Virginia when he received the call from Bellevue Hospital Center in Manhattan, the day before the Fourth of July. His son was on the line.

“He said, ‘I was in Central Park, and I stepped on a bomb,’” Mr. Golden recalled.

His son, Connor Golden, a 19-year-old college student, would lose his left leg below the knee.

Not long after the blast, Mayor Bill de Blasio sent out a message on Twitter, warning against using “fireworks.” The police would later say the explosion may have been an “experiment” on the part of a “hobbyist.”

That explanation leaves Connor’s father unsatisfied.

“Who plays with this kind of volatile compound as a hobbyist and just leaves it laying in the park?” Mr. Golden said in his first lengthy interview on the issue. “If you wanted to experiment or play with explosives, to do something like that in one of the most popular places, one of the most watched places in the country — that would be the last place you’d go. You scratch your head and say, ‘That explanation doesn’t ring true.’”