As I understand it, the primary evidence that Bulger was NOT a rat hinges heavily on the state of his FBI file.Supposedly it contained a fraction of what it should have for someone who informed as long as he did. Further, the file is riddled with "doubles", that is, the same piece of information filed more than once to pad the file out. They also contend that most of the files are extremely vague, using circumspect language as to avoid actually incriminating anyone.

It could be that his handlers tried to expunge files that made Bulger look like a rat, or it could be that they were on his pay role and thus he only gave them useless information. I don't know. But I do know his heavily redacted FBI file is highly suspicious.

Bulger was definitely a rat on paper, though. He was a confidential informant right? Like, even paid by the state to provide information?