The suspect had little money to speak of, was unable to pay his cellphone bill and scrounged for money to buy the drill bits that court papers said he required to make his pipe bombs. Initially, he had trouble drilling the small holes that needed to be made in the metal tubes.

The suspect, Jose Pimentel, according to several people briefed on the case, would seek help from a neighbor in Upper Manhattan as well as a confidential informer. That informer provided companionship and a staging area so Mr. Pimentel, a Muslim convert, could build three pipe bombs while the Intelligence Division of the New York Police Department built its case.

But it was the informer’s role, and that of his police handlers, that have now been cited as among the reasons the F.B.I., which had its own parallel investigation of Mr. Pimentel, did not pursue the case, which was announced on Sunday night in a news conference at City Hall. Terrorism cases are generally handled by federal authorities.

There was concern that the informer might have played too active a role in helping Mr. Pimentel, said several people who were briefed on the case, who all spoke on the condition of anonymity, either because of the tense relations between the Intelligence Division and the F.B.I. or because the case was continuing.