Right, but the book, which the movie is based on, goes into depth on all of that much more.
Also, people he talked with either testified about it in that hearing or were on the record in some other way. And threads where that wasn't available were investigated profusely to find if there was anything to "get him" on.
I mean, he obviously had a lot of associations and such, and there is surely a lot we don't know. But he was investigated vigorously, and most of it was drug out into public to humiliate him, so we know A LOT.
Also, people he talked with either testified about it in that hearing or were on the record in some other way. And threads where that wasn't available were investigated profusely to find if there was anything to "get him" on.
I mean, he obviously had a lot of associations and such, and there is surely a lot we don't know. But he was investigated vigorously, and most of it was drug out into public to humiliate him, so we know A LOT.