EVANSTON --Police are questioning three people about an armed robbery on the Northwestern University campus in Evanston over the weekend.Two female students were robbed at gunpoint by three men. It happened early Sunday morning as the victims walked near Bobb Hall in the 2300 block of Sheridan Road. The women were not hurt. Chicago police arrested three men a few hours later during a traffic stop on the city's North Side. Two of the men matched descriptions of the robbery suspects. No charges have been filed.