The Montgomery County Commis- , sioners, meeting today, offered $500 reward, while the Capital Transit Co. yesterday offered a reward of $1,000.Meanwhile investigators were hoping that the few meager clues they have may aid in a solution. These include bullets, recovered from woodwork in the office and from the heads of the two dead men—Janies M. Mitchell. 59. 2216 Thirtieth street southeast, depot clerk, and Emory Smith. 40. of Bethesda. Md.. barn mechanic and watchman, who was kidnaped from the scene and thrown in Rock Creek. Also, police have several : empty shells, ejected from the robbers' . pistols when fired in the station, and J measurements of footprints which ledfrom an automobile which had beenparked in the snow near the scene of the robbery.Former Employe Held.One of the men under arrest is a former employe of the street car company, who. it was learned today previously was arrested for questioning in connection with a Washington hold-up. At that time Mitchell is said to have aided in the arrest ihrough identifying the man to District detectives. The man gave himself up ar police headquarters when he learned he was wanted.