Whitey was public enemy number 1 until Osama bin Laden took that position from him while he was on the run. He went on the run after being tipped off that he was about to be arrested by the Massachusetts state police on numerous changes including racketeering, extortion, murder, etc. He was most likely tipped off by former FBI agent “Zip” Connelly who protected Whitey and the Winter Hill gang because Whitey was tipping him off about members of the Boston mafia and the Providence Mafia. Many of the members of those mafia organizations were convicted of numerous changes and sentenced to long federal prison sentences.
Whitey, in effect, had used the FBI to dispose of his criminal competitors.
And who was the Assistant US Attorney in Boston when Whitey Bulger was feeding information to the FBI? You might have heard of him. He later became a director of the FBI and is currently a special US attorney—a bum named Robert Mueller.