I lived in that neighborhood for years in the 60s and 70s and to the best of my knowledge any cemetery that existed there is nothing you'd actually call a cemetery, so I went and looked. It's a gentrified park in a former lower working class neighborhood bordering on "Alphabet Soup" that was forcibly converted to yuppie heaven. SOMEONE is pissed about that and wanted to scare the hipsters infesting the hood. Rr Ryan Carboni wrote:

https://search.wikileaks.org/gifiles/emailid/1327639

New York police discovered a trash bag containing around 4.5 kilograms (10 pounds) of what has been described as C-4 explosive in a Manhattan cemetery the morning of Oct. 11. The material did not present an immediate threat, as it was not primed with a blasting cap - a component required to successfully detonate the explosives - or a firing train for initiating a blasting cap. The New York Police Department's bomb squad has reportedly secured the material, but the area around Marble Cemetery in East Greenwich Village on 2nd Street between 1st and 2nd avenues remains closed to traffic.

It is difficult to imagine an innocent explanation for how six to eight blocks of apparent plastic explosive (likely comprising about 3 to 4.5 kilograms) came to be abandoned in the cemetery. Since the material was not primed, it does not appear to have been in the final phase of deployment for an attack. While information is still preliminary, there are a number of potential reasons for the material's presence in the cemetery. It is possible that the explosives were left there as a dead drop, to be passed to someone with bombmaking experience to construct an explosive device. It is also possible that it was simply abandoned there by someone who wanted to dispose of it. Since C-4 is a military-grade explosive, it is likely that the material can be traced back to establish where it was made, who bought it and when, which would provide clues as to how it ended up Manhattan.

A number of nations manufacture C-4 and military-grade plastic explosives similar to C-4, such as PE-4A. The New York Police Department and its U.S. federal law enforcement partners in the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives will certainly be working overtime to attempt to determine the provenance of these explosives in order to discover who placed them there and why, in addition to testing the material to verify that it is in fact explosive and not a hoax. If the recovered explosives were still in their wrappers with lot numbers affixed, the job of tracing them will be easier. However, if they were U.S.-manufactured explosives that had been stolen or captured in a war zone, the trail may be hard to trace. If the explosive blocks did not have wrappers with lot numbers, a chemical analysis of the explosives should help the authorities narrow down the possibilities.

New York remains one of the highest-profile targets for terrorist attacks in the United States, and plots to detonate explosives there are regularly investigated and disrupted. The last such plot was the failed May 1 attempt to detonate a car packed with a poorly constructed explosive device in Times Square. Indeed, many of these failed plots, like those involving Najibullah Zazi and Faisal Shahzad, failed for want of real explosives. This amount of plastic explosive would be enough to construct a relatively small improvised explosive device if it wound up in the hands of someone who wanted to use it violently, possessed a detonator or two and had some basic explosives training, but it would not be enough to create any large-scale damage by itself.