Here is are the proceedings from Nightingales original Court Martial.
http://www.judiciary.gov.uk/Resources/JCO/Documents/Judgments/nightingale-proceedings-0607112012.pdf
The following exchange is revealing...
JUDGE ADVOCATE: So Mr Winter would it be right that at the time of the interview at the latest he seemed to have regained his memory as to how he came by the Glock?
MR WINTER (for the defence): He may have done or he may have confabulated, that is the problem. By his plea we have accepted that he has regained a memory of having received it in Iraq but he does not know and the science is not sufficiently sophisticated to be able to say one way or the other, but this board is to proceed upon the basis that that is in fact an accurate memory for the purposes of this sentencing hearing and therefore is an honest and true confession. //
He seems to have been in possession of a pyrotechnic device which was not added to the list of charges.