Deputy U.S. Marshal John Ambrose was found guilty Tuesday of leaking critical information about a star witness in the Family Secrets case.

This marks the first time there was a breach in the federal Witness Protection Program.

More to come.

Here are the 16 reputed mobsters that the FBI considered the top threats against mob killer turned government informant Nick Calabrese:

1. Michael Marcello
2. Frank "Toots" Caruso
3. Aldo Piscitelli
4. James Inendino
5. Michael Sarno
6. Michael Spano Sr.
7. Paul Spano
8. Joseph Andriacchi
9. Joseph Lombardo
10. Alphonse Tornabene
11. Rudolph "Rudy" Fratto
12. Peter DiFronzo
13. Michael Magnafichi, born 2/16/52
14. John Matassa
15. Dino Marino
16. Anthony Zizzo

The list was part of the government's 2002 application for Calabrese to be allowed into the federal witness protection program.

Reputed mobsters Frank Caruso, James Inendino and Peter DiFronzo were among the people the FBI considered threats to the safety of mob hitman turned federal witness Nick Calabrese.

The revelation came today during the testimony of FBI Agent Michael Maseth in the trial of deputy U.S. Marshal John Ambrose, who is on trial for allegedly leaking key details about Calabrese to the mob.

Ambrose, who guarded Calabrese as part of a security detail, has said he made a mistake by discussing information about Calabrese with a family friend but had no intention of the information making it to mobsters.

Calabrese began cooperating with the government on Jan. 15, 2002, after agents confronted him with DNA evidence linking him to a mob murder. Calabrese eventually admitted to committing 14 mob murders and provided the feds information about another 22 Outfit hits.

On Aug. 27, 2002, Calabrese was admitted into the federal Witness Protection Program while still in prison.

Government officials had to submit an application for Calabrese to be accepted into the program, and part of that application was a list of people who posed a threat to him

There are cooperating witnesses, and then there are cooperating witnesses.

More light was shed Tuesday on the nature of Marcello's cooperation with federal authorities in the case of John Ambrose, the deputy U.S. marshal accused of leaking critical information about a star witness in the Family Secrets case to the Outfit.

While it's clear from a defense filing that Marcello, the half-brother of one-time Chicago Outfit boss James Marcello, has been talking to prosecutors about what he knows about Ambrose, he's not going to willingly take the stand.