New York City police are piecing together events behind an explosion aboard a crowded subway car in Lower Manhattan this afternoon that injured 37 people, four of them critically. The blast occurred about 1:30 p.m. as the train sat in the downtown Fulton Street station, sending hundreds of passengers rushing through opened doors without bags, briefcases and purses, some swatting away flames that caught others' clothes. Police now say an incendiary device -- a glass jar filled with flammable liquid and fitted with an external igniter -- apparently went off in the lap of a passenger in the sixth car. FBI investigators joined the search for a culprit, which now centers on the questioning of a victim found two stops away in Brooklyn suffering from severe burns. CBS News reported that police have searched the suspect's home and found bomb-making gear there. New York Mayor Rudolph Giuliani arrived at the site about an hour after the explosion, and victims wearing oxygen masks lay on stretchers one block east of the World Trade Center, where a 1993 terrorist blast killed six people.