In the mean time Billy was fully reinstated, paid-up, and actively engaged in researching Sullivan, while Dignum was busy trying to spy on Sullivan. It also meant that Billy could move out of the cell block and, after getting back his car, into constantly changing motel accommodation.
However, nemesis was not long in coming. As soon as Billy began investigating Sullivan's case files, he noticed a discrepancy. There were things about Sullivan's first major case that did not add up. Sullivan claimed that some minor hood had disposed of the Providence Mafia hit men, but Billy knew that Costello had removed the Providence hoods who were out to get him. Under interrogation the source of Sullivan's information claimed to have never met Sullivan. Could Costello have been helping Sullivan with more than just cash ? However, there was no proof that Sullivan was financially on the take. When Billy started checking up on Sullivan's rapid promotions the even more rapid promotions of Barragan became apparent. And then Billy learned that Sullivan and Barragan where both colleagues and friends at the Academy.
Soon after, FBI auditors alerted by Queenan reported that Barragan could not account for all of his car payments. Barragan was arrested and under interrogation revealed that he had been helped by Sullivan, although he denied taking bribes. No one believed this. Barragan was suspended, demoted, and was now under the standard surveillance appropriate to defrocked cops who had not been dismissed.
Sullivan had been lying low, which is why Dignum's surveillance had not managed to learn anything, yet. With the discovery that he had helped Barragan, Sullivan began to feel uneasy. He had underestimated Costegan. The gutter rat was a dangerous and persistent opponent. Now that they knew that he had helped Barragan out, how long before Costegan figured out that Costello had been helping him. The rat might guess it already. Of cause, he must. Damn, it was Barragan's rapid promotion that had alerted the rat. But proving it was another matter. But how to escape. Costello would hardly just let him back out, and now that the Feds had owned up to protecting Costello, they might go after Costello. And then Costello would do a deal. Costello had to go.
Then Sullivan was interviewed about the Providence Mafia hit men. Although no charges were made, Sullivan could read Dignum's voice and body language enough to know that Dignum knew something. Costegan had just stood there, yet like a bomb about to go off, and his body language was silent as the grave. It was a warning, and when Sullivan learned from the rumour mill that Costegan knew the truth about the killings, it was time to jump ship, fast.
Soon after Billy found Madolyn at the SIU trying to find him; Billy duly spent an extensive session at the maternity ward when his son was born. Billy wasn't really happy about staying in Sullivan's old apartment, it was too expensive and high class for him, but his family would be safe from Costello.
Billy's knowledge of Costello's behaviour and methods proved very useful. Gradually the net closed. Billy persuaded the older gang member, who had once been an FBI informant, to make a deal. Costello was crippled in a police raid lead by Sergeant Billy Costegan a year later. Too ill to stand a prolonged trial, Costello got off with minor sentencing, but without Mr French to back him and following the seizure of his assets his gang land hold was broken. Costello's archives only came to light after their Statute of Limitations expiry date.
They didn't find Sullivan until ten years later, when Captain Dignum with the help of the NYPD and the FBI collared him in connection with Jordan Belfort's fraudulent wall street share dealing. And even then the charges were minimal, Sullivan was just too adept at spinning excuses.