The NYPD bomb squad sped from the scene with the evidence safely packed in a disposal truck and rolled-up First Avenue with a highway patrol escort.
It left residents to wonder how a powerful cache of explosives ended-up in their neighborhood.
Emergency Services Unit officers responded to the scene around 10:45 a.m. Monday after a worker called 911 to report a black bag found at Marble Cemetery in Manhattan's East Village.
The eight blocks of C4 explosives were not capable of detonating, police said. Its discovery triggered a police response including aviation, emergency service and the bomb squad. The plastic explosive is used in demolition. The substance is more powerful than TNT but requires a second piece for detonation. Police said there were no extra pieces, or caps, at the scene.
NYPD Commissioner Raymond Kelly said the bag of explosives had been dug up by a caretaker in May or June 2009 while planting bushes.
He had placed the bag next to the tree, which apparently remained there untouched until Sunday.
A volunteer working at the cemetery found the bag on Sunday and looked inside to find what appeared to be explosives.
He placed the bag into a garbage container. After talking to acquaintances who informed him that the discovery could be dangerous, the man called police.
The commissioner told reporters the explosives were military-grade.
But, it was not immediately clear whether they were military-issue or available for civilian use in demolition.
Investigators say it was not a bomb and there was no detonator, but the explosives could have done enormous damage.
By apparent coincidence, a threatening note was found on the windshield of a police car at a nearby precinct on Sunday.
"The note is a rambling note that makes some reference to Second Street and has some religious statements in it, but investigators see no connection at this time," Kelly said.
Kelly said investigators were also looking into writing found on a nearby sidewalk.
"It's a statement that says 'I really hope one of you find this,' The significance of that statement, we are not certain," Kelly said.
Streets around the area remained closed on Monday afternoon as officials investigated.