At the end of February, a 300-page report, tersely titled, “New York Systemic Corruption,” was received for review by the Justice Department’s Office of the Inspector General in Washington. In three bound volumes, it detailed a series of oft-made, and explosive, allegations: that in the 1990s, while trying to stem the Colombo family war, federal prosecutors and agents for the Federal Bureau of Investigation in New York knowingly allowed two moles in the mob to kill while they were on the government’s payroll.

But the dossier had not been sent to Washington by one of the defense attorneys or professional private detectives who have, for two decades now, been working on the legal cases related to the war, an internecine struggle from 1991 to 1993 that resulted in a dozen deaths and more than 80 convictions. It was sent from an unlikely, and mostly unknown, source: a 5-foot-4, single mother from New Jersey named Angela Clemente.

For nearly 15 years, Ms. Clemente, 48 and a self-professed “forensic analyst,” has waged an independent and improbable campaign to prove that the government turned a blind eye to as many as 39 murders committed in New York by turncoat gangsters it paid to work as informants.

Through interviews in the underworld and by prying loose documents from classified archives, her unusual citizen-sleuthing has taken her deep into the local version of the James (Whitey) Bulger case, which is now being tried in Boston. Not only into the annals of the New York mob, but also, in a strange, octopus-like fashion, into corollary inquiries into Islamic terrorism, the Kennedy assassination, even the 1995 bombing of the Alfred P. Murrah Federal Building in Oklahoma City.