A passenger was shot dead in a Manhattan subway (search) train as passengers screamed and dropped to the floor for cover.

Investigators believe Tuesday's shooting stemmed from an earlier dispute between two men who fled the scene and the victim, Nelson Stanford, who police said had an extensive criminal record.

It was the third shooting in the subway in the last month. The other two victims survived.

Police were searching for two suspects Wednesday and had made no arrests, said Sgt. Michael Wysokowski, a police spokesman.

The victim and the suspects boarded the train at a station in the city's Chelsea neighborhood (search), police said. At the next stop, up to four shots were fired, and Stanford fell face down as passengers screamed, witnesses said.

Stanford had several prior arrests on attempted murder, drug possession and other charges, police said.

Earlier this month, model-actress Monica Meadows (search) was shot in the shoulder on a subway train in Times Square (search). David Hart, a business school chief executive, was shot in late May as he walked through a subway turnstile in Queens.