My friend didn't let my dog out for 2 days. what would you do or say?

We just got back from a hunting trip. My dog ran out and took a monster piss and had sloppy poop. (Sorry) I thought, "What the hell?!" A friend (I'm not so sure now) said he would come before and after work to let our great dane out to go to the bathroom. We left a note, a key in the BBQ, treats and a chew toy on the stove. We got home and the note was still in the door jam, the treats were still there and they key wasn't touched. We weren't sure if what we were seeing was true. We knew he was flakey, but not negligent.
My husband called and played it cool since he didn't want to jump to conclusions. He thanked him and started sort of quizzing him. But the more he talked and asked questions about how it went, we think we're sure he didn't come. He was very vague with answers, like "Oh yeah." or "nope". Turns out he was in the car with his wife who we could tell, she didn't know he volunteered to help us. I could hear her over speaker phone saying "Oh, they left? Where did they go?" He said "They went on an elk hunt" and she said "Oooh cool, did they get anything?"
They only have one car right now and she drops him off and picks him up from work so she would have had to have know for sure since she drives him. She is a vet tech and an animal lover and I know if she would have known she would have been more than happy just to take her to her house while we were gone.
There is more and more evidence proving he didn't come. Lucky she didn't go in the house. Poor dog!!
Knowing him (so I think) our thank you and gratitude will eat at him and he always eventually comes out with the truth of whatever it maybe...eventually. A couple hours after my husband called, knowing his wife would castrate him if she found out, I texted her...."Hey you two! Thank you so much for letting Lily out while we were gone. We really appreciate it!" I also texted it to him....because if he really did come (which I doubt) then he can't be mad at me for throwing him under the bus.
My husband said he thinks it will eat at him for a few days and he might call. If he doesn't call in the next couple days he said he would call him and ask him for the truth.

I am so mad. I am glad my dog is okay and she didn't make a mess. But if any of you have a dog and no kids, you know how much that really hurt our feelings. We don't want to jump the gun. We'll give him a couple days and them ask him pretty much...where our friendship should go after this. He's been a bad friend lately and neglecting an animal, and our 'kid' was the nail in the coffin. In a mean way I think it's funny I texted his wife. I know how nasty she can be.
When my husband calls him he's planning on saying "I know you were lying. I just wanted to see if you were going to be honest." And "Why didn't you just say 'no' if you didn't want to?"

When he was on the phone I yelled jokingly, "She POOPED IN THE HOUSE!" I heard him over the speaker saying, "oooooohhhh." In the 'I wouldn't be surprised' kind of way.

AAAAnny way blah blah blah...
We're both pretty sure we're done being friends with this guy. We don't want a huge confrontation, just an understanding why he would do such a thing before we sweep him under the rug.

What would you say if you were to call him back?
What would you have done?

Should we just leave it at "Hey thanks!" and let it eat at him? And then politely disconnect with him?