I'm sure he is a good man, but he f^cked up. He could have taken the piece back to work at any time in the 24 months+ and declared it - no questions asked. If he wanted to keep it, there are plenty of people that could have decommisioned it, certificated it and then he could have mounted it on his lounge wall if he wanted to.
As for raiding "any of us who have been on Ops in the past 100 years" - feel free, you will find no firearms/explosives in my household. However, standby for a strongly worded note from my solicitor for compensation for the stress you put my family under - so you'd better have pretty good grounds for suspicion!
I suspect he will be out a lot quicker than the 18 month sentence, but maybe it will serve as a reminder to those that decide to do stuff like this "in the next 100 years" not to do it.
iRaven