Exampe:-
Name the prisoner: POW
Name your group leader: W1
Put a trigger over him act for Blufor and in the on act:
[POW] join W1
When you want to drop the POW off in another trigger act for Civ onact:
[POW] join grpNull
If the POW is BLUE
Hope this helps.
p.s if you want to make it an add action rather than a trigger I can also help