Actually, liars often have well rehearsed routines. Consistency is no indication of truth.
Yes as in most things with this case he could be prolific with his letters to try and get people on his side to try and prove his innocence - or as others have implicated he could just be attention seeking .
He obviously trusted CAL though .
And in her book to be fair she did not seem to try and influence the reader with her own opinion . she has said this herself.
It is only with the drama promotion that her guilty stance has been drawn attention to .