Bill was a good guy he did what he had to.. to survive (spoiler)

...in '73, his role as an informant was discovered and he was relocated under the Federal Witness Protection Program to California...He reportedly returned to the Chicago area in the 80s after the tension of living under witness protection led to him splitting with his first wife. Speaking with the Tribune in '84, O'Neal said that while he had thrived working with law enforcement, he ultimately felt he’d been ''just a pawn in a very big game.''

...O’Neal did have a relationship with his uncle, Ben Heard....he was at Heard’s home having beers on MLK Day just before his death. Heard said that night his nephew kept leaving to use the bathroom: "He'd stay in there 10 or 15 minutes. The last time he stayed 20 minutes. He came out in a rage and he tried to jump out my living room window” he told the Chicago Reader. “I stopped him. I grabbed him by the ankles. I wrestled with him but he broke free and he ran out the door.” O’Neal then bolted onto a nearby expressway, police said. His death was ruled a suicide by the Cook County Medical Examiner's Office. He was 40.

After his death, an interview O’Neal had sat for in April 1989 with the public television series ''Eyes on the Prize II” aired in Chicago. ...he began to shift in his chair while discussing the moment back in 1969 when he re-entered the scene of Hampton’s killing. With a distant look in his eyes, he began to express a sense of contrition. “I just began to realize that the information that I had supplied leading up to that moment had facilitated that raid,” he said. “I knew that indirectly I had contributed — and I felt it, and I felt bad about it. And then I got mad. And then I had to conceal those feelings, which made it worse. I couldn't say anything. I just had to continue to play the role.”

BTW, per Newsweek:

In a title card, Judas and the Black Messiah implies that the release of Eyes on the Prize II was linked to Hampton's suicide, noting that the show started airing on the same day that he ran into traffic. However, the episode about Hampton did not air until February 19, 1990.

By all accounts, he was piece of shit sell out who probably died a thousand deaths in his own mind over what he had done before he finally had the guts to off himself.