I am repeating myself here, but IMHO Fredo could have never "come clean" because by doing so he would have had to reveal he knew it was going to be a hit, and that it was he who let Manolo in to open the drapes.

"Io sono stanco, sono imbigliato, and I wan't everyone here to know, there ain't gonna be no trouble from me..Don Corleone..Cicc' a port!"

"I stood in the courtroom like a fool."

"I am Constanza: Lord of the idiots."