In the novel, Tom went up to New Hampshire to talk Kay into returning to Michael after she left him because she figured out he lied to her. The film did portray her as naive. It served as quite a contrast with her catharsis in II when she asks about Pentangeli, etc.

As Lilo says, Mike wasn't going to admit murder to Kay. What wuld be the percentage in it? Besides, By itself, it would be hearsay, but it could be used in a criminal prosecution.

"Generosity. That was my first mistake."
"Experience must be our only guide; reason may mislead us."
"Instagram is Twitter for people who can't read."