My Best-friend's husband stole something from me, what should I do?

My best-friend of 15 years was feeling down so I invited her, her husband and kids over for dinner. We were all in the kitchen when I noticed my friend’s husband picking up my pocket knife off of the floor look at it interestingly and I think he placed it on the kitchen table. I say “think” because I didn’t really watch his every move since I figured he was trying to keep it off the floor and out of the 2 year old’s hands that was walking around and being curious.
The next morning I went to look for my knife and I could not find it, I moved a few things around and couldn’t find it, I didn’t do a complete and thorough scan of the table just because I figured since he had just picked it up it should have been just placed there in plain view. I plan to go home tonight and do a more thorough search and be certain it isn’t there.
What should I do if I don’t find it?
I would like to casually ask her like “Hey, I was looking for my work knife this morning and I remember _____ had moved it onto the kitchen table out of baby’s way, but maybe he placed it on a shelf somewhere because I couldn’t find it this morning on my way out. I was kinda in a hurry so maybe I missed it or something?”
This seems like I’m not assuming anything but letting her know that I saw ______ with it last. There is no way that anyone else grabbed it, and I wonder is it that important to possibly risk ruining a friendship if she covers for him, which I think she might out of embarrassment. I really don’t think I will get my knife back and I really liked it, but I’m not sure it’s worth possibly losing a friend either though. But then again what man of age 33 steals from a friend?