This has been nagging at me. I am assuming it means he wanted out, due to his upcoming wedding, and feared they might not let him out.
Harbour may have feared Brown would go to the authorities, and went to confront him. Maybe he feared that if he waited until after the wedding, and the honeymoon trip from which Brown might not return, it would be too late.
Somebody stop me, I'm on a roll here.
I still like my "grand unified theory". A dealer in surplus military parts is in a perfect position to trans-ship high-tech weapons systems to third countries, with or without official approval. It takes an approved military surplus dealer, and someone on the inside to certify the equipment as "surplus". Oh, hey, maybe someone like a civilian lawyer for the Joint Forces Command.
Forget that theory. Everything they sell is demil parts from government. Anyone could buy that stuff