Police Still Investigating What Caused Explosion in Central Park

— -- Police are still investigating the explosion in New York City's Central Park this weekend that seriously injured an 18-year-old college student.

Connor Golden of Fairfax, Virginia, was climbing rocks in the park Sunday morning with two friends when the explosion occurred, severely injuring his foot.

His family told ABC News that his left foot has been amputated. He's in serious but stable condition.

"His life will never be the same," his grandmother Roberta Golden said.

New York Police Department Lt. Mark Torre said there's no indication the blast was terrorism-related.

"What seems likely at this point is that we have ... an explosive hobbyist or an experimenter," Torre said. "I believe we have somebody that made this material and then he wanted to test it."

He added, "If somebody lives in that vicinity, their backyard is Central Park. It's sort of an ideal location conducive to conducting that kind of experiment."

Officials stress that Golden and his two friends are not considered suspects.

Besides the motive, the explosive material used in the blast remains a mystery; lab results for the explosive material are due Wednesday.

While people are "on edge" in the wake of terrorist attacks around the world, ABC News contributor and former NYPD Commissioner Ray Kelly said that "this was perhaps a chemistry student, something along those lines, trying to make fireworks for the events on July 4."

Investigators will "do a lot of checking on the internet — see if there are groupings of people that perhaps talk about making fireworks, that sort of thing," he said.

According to Steve Ganyard, an ABC News contributor who is a former deputy assistant secretary of state and a retired colonel in the Marine Corps, the explosion was "concerning" and may not be "as benign I think as the police are making it out to be. It's something that we need to consider as a domestic terror incident."

He continued, "We have lots of premeditation. This is somebody who went to lengths to create a dangerous explosive material. So Fourth of July, public place — I think we need to keep this as an open question about what the motive and what the intent was."