Military-grade explosives that sparked a massive police operation at a historic New York cemetery were dug up by a caretaker last year and left at the site, it has emerged.
The explosives, similar to the material used in the 2005 London bombings, remained at the cemetery in a plastic bag until a volunteer told authorities about it on Monday.
The employee found the C-4 explosives last year after digging down about a foot into the ground at New York City Marble Cemetery on Manhattan's Lower East Side, New York police commissioner Raymond Kelly said.
It contained eight sticks of the explosive, but Mr Kelly said they could not have gone off because there was nothing to detonate it.
It was unclear how long the bag had been at the cemetery, but "we believe it's been there for a significant period of time", Mr Kelly said. He ruled out any terrorism connection to the discovery.
The caretaker left the bag on the property, by a fence in the back. A volunteer came across it over the weekend, and initially also left it there before calling police. Authorities sealed off nearby streets as they investigated.
C-4 is a plastic explosive that is more powerful than TNT. It's commonly used by the military because it is easy to shape and relatively hard to set off by accident. C-4's main ingredient is RDX, which is also used in fireworks.
It is relatively insensitive to impact, friction or fire, although large quantities can explode if burned. Even shooting it with a rifle will not trigger the reaction. Only a detonator or blasting cap will do the job properly. Less than a pound of C-4 could potentially kill several people, and several blocks of C-4, weighing about 1.25lbs each, could potentially demolish a truck.
Mr Kelly said the material from the cemetery was being taken to the police range where explosives are tested. Authorities also were digging around in the cemetery to see if any more material was found.
Police were also looking into two messages that were found in the area to see if there was any connection. One, written in chalk on the pavement near the cemetery, said: "I really hope one of you finds this." The other, a note placed on a police car at the precinct near the site, made a reference to Jesus Christ being kept out of the neighbourhood, and was signed by someone identified as "Jesus Christ".