All of those things, as stated earlier, reflect poorly. Convicting someone of a crime should be on the basis of an accusation by a named, identifiable accuser who can be confronted by the accused (subject to observation in the courtroom, of course, and intimidation and the like should be strictly disallowed), not something else. One should never be convicted or imprisoned on a basis like this: "Well who said I did something wrong?" "Well we can't tell you that, but here's a scrambled videotape of their accusation." "Well that's not true, I want to cross-examine them! And I want to know who they are, what if it's someone who has a grudge against me?" "Sorry, won't be possible."
I think the accused (and their legal team) gets to know who it is, it's just not released to the public. And I think they do get cross-examined, just from behind a screen or on a TV monitor.