THE BRONX - The National Transportation Safety Board has removed the rail workers union from its ongoing investigation into Sunday's Metro-North train derailment in the Bronx.

NTSB officials say that Anthony Bottalico, the general chairman of the Association of Commuter Rail Employees, violated a confidentiality policy that each agency involved in the probe had agreed to when he spoke during a press conference Tuesday.

Bottalico said engineer William Rockefeller caught himself nodding off at the controls prior to the derailment, but that it was too late to stop the train as it approached a sharp curve in a 30 mph zone traveling at 82 mph. Four people were killed and 63 others hurt.

The NTSB said in a statement, "While we value the technical expertise that groups like ACRE can provide during the course of an investigation, it is counterproductive when an organization breaches the party agreement and publicly interprets or comments on the investigation information."

NTSB officials also spoke during a news conference Tuesday, revealing more information about the accident. Member Earl Weener said it was too soon to say whether the accident was caused by human error, but that investigators found no problems with the train's brakes or rail signals during the nine stops it had already made.

Several published reports have cited that Rockefeller told officials at the scene that he "zoned out" moments before the derailment. He was more than two hours into his shift, which started at 5 a.m., at the time.

Rockefeller, 46, has worked for the railroad for about 15 years and has been an engineer for about 10. The rail union says he was injured in the wreck and has cooperated with the investigation.