Updated at 2:00 a.m. ET Wednesday:

Federal investigators in New York announced late Tuesday that they had removed the rail employees union, the Association of Commuter Rail Employees, as a participant in the investigation. According to The Associated Press, investigators cited a breach of confidentiality after Anthony Bottalico, leader of the union, spoke to the media concerning comments train engineer William Rockefeller had made about what happened moments before Sunday's derailment.

Update at 8 p.m. ET:

The Associated Press reports:

"The engineer whose speeding commuter train ran off the rails along a curve, killing four people, nodded at the controls just before the wreck, and by the time he caught himself it was too late, a union official said Tuesday."

"William Rockefeller "basically nodded," said Anthony Bottalico, leader of the rail employees union, relating what he said the engineer told him."

"'He had the equivalent of what we all have when we drive a car. That is, you sometimes have a momentary nod or whatever that might be. How long that lasts, I can't answer that.'"

"Rockefeller's lawyer did not return calls. During a late-afternoon news conference, federal investigators said they were still talking to Rockefeller, and they would not comment on his level of alertness around the time of the Sunday morning wreck in the Bronx."

From our earlier post:

There is "no indication the brake systems were not functioning properly" when a New York City commuter train derailed Sunday, National Transportation Safety Board member Earl Weener told reporters late Tuesday afternoon.

The mishap killed four people and injured more than 60 others.

Weener, who on Monday said investigators had determined the train was traveling at 82 mph when it went off the rails — on a curve where the speed limit was 30 mph — released some other information Tuesday about the investigation so far:

-- Tests of both the engineer and conductor indicate alcohol was not involved. The results of drug tests have not come in yet.

-- The engineer was a 15-year veteran and had regularly been at the controls for two round-trips a day on the route from Poughkeepsie to New York City and back.

-- Tests of the brakes before the train departed for New York City found "no anomalies."

Investigators have not determined if human error, mechanical failure or some combination of the two caused the derailment.

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