Well,
I will describe something that happened at the end of WW2 to me.
After the British Army har relieved some towns and cities in Germany,we suddenly has seconded to us (per regiment) about 10 "advisers".
These guys were supposedly to give advice to the Army about Rationing,nutrition,rebuilding,social welfare etc.
However,they never seemed to be giving advice to ANYONE about ANYTHING!
I approached my commanding officer and enquired about this.He was a good chap and told me (discretely) tha they were actually from the Secret Service Bureau (forerunner to MI5 & 6) and were really there to "spy" on the German population so as to find war criminals.
I am not saying these hostages WERE doing that,but I believe they were doing something underhand and shady,that we are not supposed to know about,OR even question!