This is story I actually know something about. I knew Shane personally and attended many BBQ's with him and the various other people that made up the explosives team.
I have for obvious reasons not had any contact with him since the incident.
I can even provide what I am very confident the reason for why he did it. He fully knew what he was doing, and indeed the reason was for money. However not for selfish reasons. A captain salary is not that fantastic in the army and his wife at the time, whom I suspect he is separated from now liked to live fancy. In fact I am 100% confident it is because of her that he did it. Probably without her being involved, but I cannot be sure of that. I do know she overextended their finances which would have been a good motivator.
Any claims he made to forget destroying them are a horrible attempt at deception to reduce his sentence.
For what its worth he was ostracised from the explosives community over this. It was a very small group of people, and Shane's appeals to have them speak on his behalf were ignored by them all. The group is very tight and for one of their own to betray was seen as a massive abuse of trust.
Honestly I was very sad to hear it. Selling out your country for the low amounts he did is such a sad thing. I don't think he needed to be in the super max prisons he spent his time in as I don't believe him to be a dangerous person. Certainly a very stupid mistake, but not a dangerous person. I suspect most of his being incarcerated in such was as a message. Personally I remember him as a fun person at a party enjoying a few beers and telling amusing stories of which there were many.
As for if other weapons are missing. That is possible. Shane was tasked with destroying them. Its much harder to steal from stores due to them being tracked quite well but those to be destroyed are much harder to keep track of. Usually there would be several people involved to help avoid this sort of incident.