They began digging around 8:00 Monday morning along the Hudson River and near Palisade Avenue and Spaulding Lane in Riverdale.
A tip on an old homicide case, maybe a decade old, led investigators to the location inside Alder Brook Park.
Sources tell Eyewitness News that agents are looking for a body that may be buried here.
The unusual activity startled those who live nearby and frequently use this park.
"I mean, it's upsetting to find that there may be a body buried down there," Margie Gayton said.
Dogs brought in to help with the search apparently smelled something, but more than 5 hours of digging turned up nothing.
Agents taped off the park to visitors and suspended the search for the day.