By DEANNA BOYD FORT WORTH A 27-year-old man already in custody on allegations of robbery now faces a charge of murder in the deadly assault on a homeless man.Raymond Arredondo is accused of beating Steven Koran, 49, on Friday at a camping site where Koran and a friend lived.It resulted from an argument between the victim and another man, who then recruited Arredondo to beat up the victim, said homicide Sgt.