Chicago Police spokesman Martin Maloney says officers arrested a suspect a short distance away after today's shooting and recovered a weapon.
The shooting occurred at the LaSalle Street Blue Line station, near the Chicago Board of Trade building in the city's financial district.
One witness, John Langston, says the first car of the train was hit. He says four or five shots were fired, and sounded like blows from a sledge hammer. Langston says spent shell casings littered the platform.