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The 24-year-old man charged with killing a senior leader of the Gambino crime family in Staten Island told detectives that he was high on marijuana and shot the crime figure because he feared for his life, according to two law enforcement officials with knowledge of the matter.

But the man, Anthony Comello, gave several conflicting accounts about what happened the night the reputed mobster, Francesco Cali, was fatally shot, and investigators have been unable to corroborate many of his statements or to establish a motive for the shooting, the officials said, speaking on the condition of anonymity to discuss an open investigation.

At an initial court appearance on Monday afternoon in Ocean County, N.J., Mr. Comello held up a palm on which he had scribbled “United We Stand,” and “M.A.G.A. forever,” as well as a circle and “U.S.A.”