On a completely aside note, this amassing of weapons by current and ex military is far more widespread than this case alone.
Seriously, people join up for a multitude of reasons and weapon fixation has to be one. This, coupled with access above and beyond Joe public means there will be a proportion of people out there with all sorts stashed away.
^ this comes from someone I trust (and is ex forces) who in turn knows of people who have such a stash.
‘nursing a semi’ Nightingale just happened to get caught.