BOSTON - Charges were dropped posthumously against a man who died in prison after serving 30 years for a mob-related murder that authorities now acknowledge he didn't commit.

In a court motion quietly filed in September, the district attorney's office cited FBI memos showing Louis Greco, who died in prison in 1995, was set up by Joseph Barboza, a mob hit man turned government witness.

In return for his help, the FBI made Barboza the first participant in the witness protection program. Federal authorities sent him to Santa Rosa in 1969 without notifying local authorities. He gained a new name - Joseph Bentley - and a new vocation: ship's cook.

But Barboza continued a life of crime. He went to prison for killing Clay Wilson, a Santa Rosa man who had stolen stocks and bonds from a Petaluma family, in 1970.

Barboza was paroled in 1975 only to be killed months later on the streets of San Francisco - by a Mafia hit man.

The case was part of a series of embarrassing episodes involving the Boston office of the FBI, which has been the subject of a congressional probe into the FBI's corrupt relationship with its mob informants.

"It appears that justice may not have been done," Assistant District Attorney Mark Lee said in the motion exonerating Greco. The motion also cites "legal and ethical considerations raised by the newly discovered FBI documents, as well as principles of consistency and fundamental fairness."

Greco always maintained he was in Florida on March 12, 1965, when Edward Deegan was gunned down in an alley. He was 78 when he died in a prison hospital of colon cancer and heart disease.

In 2000, a Justice Department task force uncovered secret FBI memos showing Greco and three co-defendants, Peter Limone, Joseph Salvati and Edward Tameleo, had been wrongly convicted based on perjured testimony.

The following year, a judge exonerated the surviving co-defendants, Limone, who spent 33 years in prison, and Salvati, behind bars for 30 years. Tameleo had died in prison in 1985. The judge found FBI agents hid testimony that would have cleared the men because they wanted to protect their informant, Barboza, who later became a star witness in three Mafia trials.

Limone, Salvati and Greco's family sued the federal government for malicious prosecution, wrongful imprisonment and other claims.