The Man Behind the Gun

Harry Potter, Age 17, runs away from his abusive family members, seeking shelter in Gringotts. There he meets the Muggle, dark Alchemist, and Ex-Soldier Gordon E. Lincoln, who had just lost his dear Witch Daughter due to a magical virus.
Unaware, that this man was eavesdropping on him and his talk with the goblins, he was shocked to find out the next morning that someone had broken in into his relatives' house and shoot them down, leaving Dudley (who was actually relieved) an Orphan.
As Dumbledore finds out who it was, Harry tries his best to protect the man behind the gun, moved by his deeds.
But what was his ambition?