I'm very new on here and am not really in a position to be giving anyone advice, but I wanted to share with you. Playing detective will drive you crazy. A while ago I decided to just listen to my gut. You'll never be able to prove he broke into the house (or he was high, or he took the money that's missing, etc), but trust your gut. You're not a court of law, you're his mother. Protect your home as best as you can (we got an alarm system and made sure every access point into the house is secured -- installed steel "things" on the door frames, secured the double hung windows that I found are amazingly easy to break into if you only have the standard lock that they come with, etc). Nothing will keep a determined thief out, but you can make it a little harder for them. The alarm system helps me sleep better at night knowing that if a door or window is opened I'll be alerted.
I hope your meeting with your son goes well.