I have to agree with danacara on this one, for several reasons:
1. You can't deny that he has had the opportunity. He is two and a half hours from home on a military base. He goes to bars frequently with his friends.
2. Whether he is or isn't having an affair, he would have responded with a denial. I bet nine out of ten women who found out their husbands were cheating on them, got the same denial when they first confronted their husbands.
3. I also bet nine out of ten cheated-on wives would have told you that they had no reason to worry and that they trusted their spouses completely. What was the cause of the break-up of your husband's first marriage?
4. I think your husband's reaction is a little over the top. I would hope he would concentrate on making sure that you are o.k. and not on fingerprint analysis and computer spying.
5. Why would someone send an anonymous letter to you? What reason would they have? The only plausible one I can see is if it was the ex-wife trying ot get back at you both for something. Otherwise, I can't understand why someone considered a "wack-job" at work would do this. Someone would have to be certificable insane in my book to do this - especially if there could be career repurcussions if they get caught.
6. Finally, I don't think you would have brought this up on the DIS if you weren't having some doubts of your own. I am sure you knew from past, similar situations aired here what kind of responses you would get.
That being said, I put a lot of faith in your trust of your DH. I don't think I would go all out and hire a PI, but I wouldn't brush this under the rug. I would do a little quiet investigation on my own. I might bring the subject up casually with people who might know something - a la "did you hear that I got this letter..." I might check cell phone and credit card bills. I would be on alert for signals that things just aren't right.
I sure hope this is nothing and I am sorry that this craziness has entered your life. Please don't take my post as an attack on you. I am just an unbiased observer coming to a conclusion based on my understanding the part of the story I have seen.
Denae