The murder

I have one question - why didn't the Teacher kill the wife, too? He kills Sal because he was the one who had the hit out on him. Then the kid walks into the room, so the Teacher chases him down the hallway and shoots him. Then, he leaves, and leaves the wife alive. Why? Also, didn't she see the guy who shot her husband? She said he got right into bed with her and Sal. Why didn't they send her to a sketch artist or something? If the Teacher had sent someone else to do the murder - how can they say that the Teacher did it? It would make him just as 'Not Guilty' as Louie Boffano was.

Also - I know they said they could dig a tunnel to Sal's house to take him out. Did they seriously dig a tunnel? Or did that just happen to be what they were talking about when he orders the hit? How could they not notice a big tunnel leading under the guy's house, and follow it back to where it started? It just seemed like a stupid thing to say and keep bringing up if he didn't really dig it. Or does it have some other meaning I'm not catching?

I've got two good posts in me and I just wrote my third...