Nearly a year after a blast in New York City's Central Park seriously injured a tourist, the case remains unsolved, forcing investigators to look for new leads.
Investigators made a public plea on Wednesday, urging people to come forward with any photos and videos leading up to last year's July Fourth weekend.
"Right now, we are still missing a lot of answers. We need a lot of information so we are reaching out to the public," NYPD Det. Chief Robert Boyce said at a news conference.
Connor Golden was visiting Central Park from Virginia on Fourth of July weekend last year when he stepped on a clear plastic bag full of readily available -- and explosive – chemicals. He was climbing down from the rock near the southeast entrance of the park when the homemade bomb went off.
Golden's leg was amputated below the knee.
NYPD and the Bureau of Alcohol, Tobacco, Firearms and Explosives have reviewed thousands of hours of video and reviewed about 20 tips from the public to pinpoint the culprit, but with no luck. Boyce said they need more to crack the case.
"Specifically, we are calling out visitors in Central Park to come forward with videos and photos of the rock formation," Special agent of the ATF Ashan Benedict said.
"We need the public's help by providing us with photographs and video taken at the location of the explosion in the days and weeks prior to July 3, 2016. Any person who may have any other information regarding the explosion is strongly encouraged to contact ATF or the NYPD," Benedict added.
A reward up to $40,000 is also being offered to anyone with information that leads to an arrest.
Boyce said the explosive was placed several days before the incident, but it is still unclear why.
Investigators said they are looking for a "person with some sort of chemistry background" because of the way the explosive was constructed. The materials used were tested and provided some leads, but have all become a dead end.
Investigators believe the incident was not terror-related based on the evidence they have, Deputy Commissioner of Intelligence and Counterterrorism John Miller said. Similar compounds used in the homemade bomb have been used in terrorist attacks abroad.
"We've seen compounds like this used by terrorists," Miller said, but continued by citing examples of situations that were not terror-related.
Miller added that the explosive bag was placed 50 feet from the main road on one of the busiest weekends in Central Park and New York City.
Initially, city officials said the explosion was caused by a homemade firework set off during Fourth of July weekend, but the lack of fuse or device indicated otherwise.
Katherine Lam is a breaking and trending news digital producer for Fox News. Follow her on Twitter at @bykatherinelam