About 400 people marched in Dallas, Tex., from the John F. Kennedy Memorial to City Hall and back in support of the beleaguered Police Department in the wake of the shooting death of a white policeman by a black vagrant. Some carried signs reading "God Bless Our Men and Women in Blue" and "Police Are People, Too." The shooting Saturday has heightened tension between the mostly white department and the city's minority community. Meanwhile, police Capt. John Holt said officers were trying to identify the two to 10 onlookers who, according to witnesses, yelled "Shoot him, shoot him," encouraging the vagrant, Carl Dudley Williams, 34, to shoot Officer John Chase, 25, after he took Chase's revolver. Williams, who later was killed by police, had a history of mental problems.