NEW : Train was returning to yard after being cleaned of graffiti , BART official says . NEW : The workers were supposed to stay clear of the track , official says . NEW : The four-car train was on a routine maintenance run with an experienced operator at the controls , but at the time of the incident , it was being run in automatic mode under computer control , BART said . One of the victims was a union worker who ` ` chose to return to work , '' official says . They were inspecting a possible slight dip in the track .
NEW : Train was returning to yard after being cleaned of graffiti , BART official says . NEW : The workers were supposed to stay clear of the track , official says . NEW : One of the victims was a union worker who ` ` chose to return to work , '' official says . They were inspecting a possible slight dip in the track .