I agree about Connie. According to the Harlan Lebo's 'Godfather Legacy' a script that was written in the mid 80s, and was ultimately scrapped, had Neri admit to Connie that he betrayed Michael and left the drapes open at the communion.
She blackmails him into poioining Michael as payback for Carlo and is ultimately killed himself.
Personally, I'm glad that neither Neri nor Tom ever betrayed Michael.