Colonel Henry Douglas is an officer at the Military Police headquarters in Central City and the man ordered to arrest 2nd Lt. Maria Ross for the murder of Brigadier General Maes Hughes.
In the 2009 adaptation, there's an exclusive scene related to the manga plot where Douglas is interrogating Ross and shows her the bullet that killed Brigadier General Hughes. He reveals that it is the same type she uses and showing her the ammo requisition form he asks why she needed to order a new one. When Ross mentions that she fired a bullet while protecting Alphonse at Laboratory 5, however, she finds there is no way to prove it since the facility was unmanned and is now a pile of rubble making it difficult to find a bullet. When Douglas brings up the fact that Ross was seen by eyewitnesses leaving the scene when Hughes was murdered, Ross finds it impossible since she was off duty visiting her parents, but the testimony of her parents or close friends cannot be considered creditable for an alibi.
Douglas reappears after Colonel Roy Mustang apparently burns Ross to an ashy skeleton, admonishing the Flame Alchemist for letting personal issues take him to such an extreme and stating that, thanks to the excessive damage, the identity of the corpse cannot be confirmed. His last appearance was in Chapter 35 when Roy and Lt. Hawkeye attempt to confuse the Military Police as to Scar's whereabouts so as to help Edward and Alphonse Elric lure out the Homunculi.
His fate still remains unknown, but it's possible that he was arrested as a conspirator.
(Source: Fullmetal Alchemist Wiki)
