The Army has ordered a thorough internal investigation into the deaths of three civilians in the Poonch district of Jammu and Kashmir following allegations that they died in its custody, people familiar with the matter said on Sunday.The three civilians were allegedly picked up by the Army for questioning in the wake of the killing of four Army jawans in an ambush by unidentified terrorists in Poonch on December 21. The three civilians, aged between 27 and 42, were found dead on December 22.