(CNN) -- The NTSB said it has booted the rail union from its investigation into the weekend's deadly train derailment for violating confidentiality rules.
The agency made the announcement late Tuesday night, hours after a union representative told CNN that the train engineer apparently "was nodding off and caught himself too late" before the accident.
The train derailment Sunday killed four people and injured 67 others in New York.
In its announcement, the NTSB specifically cited those comments as the violation.
Anthony Bottalico, the union representative, told CNN that engineer William Rockefeller Jr. recognizes his responsibility in the incident.
"I think most people are leaning towards human error," Bottalico said.
Rockefeller's lawyer, Jeffrey Chartier, characterized what happened as "highway hypnosis." He said his client had had a full night's sleep before the crash, and had no disciplinary record.
In a brief conversation with investigators, Rockefeller said that moments before the derailment of the Hudson Line train in the Bronx he was "going along and I'm in a daze. I don't know what happened," according to a law enforcement official familiar with that conversation.
Rockefeller spoke to Metropolitan Transportation Authority and New York Police detectives at the crash site before he was taken to the hospital Sunday.
According to NTSB representatives, results from alcohol breath tests for the train engineer were negative, and the brake and signal systems in the deadly Metro-North accident appeared to be working. Other toxicology results have not yet come back.
Fatigue is a factor being investigated, according to a separate New York law enforcement source. But Rockefeller also told investigators on site that the brakes had failed, as CNN reported previously. Officials noted the train had been able to stop nine times at stations ahead of the crash.
The train was equipped with a "dead man's pedal," designed to stop the train if the engineer becomes incapacitated, said National Transportation Safety Board member Earl Weener. But it was unclear whether that emergency system was activated.
Expert: "Twilight" common among train crews
Steven Harrod, a University of Dayton professor and expert on railway operations, said the early hour of the derailment, along with the decreased rail traffic on the post-Thanksgiving weekend, also could have played a role in Rockefeller's "daze."
Harrod called it a "twilight" of inattention or distraction common in transport crews on late-night and early-morning shifts.
"If he was dead, dead asleep, his hands would have come off the controls and ... some of the 'dead man' stuff would have come into play," said Harrod, referring to "dead man" mechanisms that automatically stop trains when the engineer is incapacitated. "But if it was kind of that twilight where you're just there and still kind of gently holding onto to things but not quite really aware, which in my mind is still sleeping. That's still sleeping."
In the culture of railroad workers, Harrod said, admitting to falling asleep at the controls is almost as bad as admitting to being drunk or on drugs.
"It's very realistic that he, in fact, really did fall asleep," he said. "Falling asleep at the controls of a locomotive is a horrible evil. You're not supposed to do that. He really doesn't want to come out and say, 'I fell asleep.' It's emotionally embarrassing. It's not just a rules violation. There's a psychological component. If you come out and say, 'I fell asleep,' it's just purely beyond embarrassing. It's a violation of the sacred understanding of what a train crew should do."
Rockefeller is not working or getting paid, according to Meredith Daniels, MTA spokeswoman.
"He is out of service. This is an unpaid status," said Daniels, adding that Rockefeller is presumed innocent until disciplinary procedures are completed.
NTSB officials would not comment on Rockefeller's reported comments, but they have said fatigue is routinely investigated as a possible cause in such cases.
Harrod said the rail and signal hardware date to World War II and, if Rockefeller was dazed or momentarily distracted, there was no system in place to alert him that he was traveling at 82 mph.
"It's a perfect-storm kind of thing," he said. "You can look back in the history books of railroad accidents and there are plenty more where this came from. Events and things that happen that in and of themselves are not supposed to be bad but they turn into bad things."
Engineer cooperating with authorities
The train was about 10 miles short of its destination, Manhattan's Grand Central Terminal, when it derailed on the approach to the Spuyten Duyvil station in the Bronx.
The NTSB's interview Monday with Rockefeller was cut short because of his emotional state, Weener told CNN. The interview resumed Tuesday and was expected to continue Wednesday.
"I think it was basically emotional issues with the engineer," Weener said. The crash, which took four lives,
was "a very traumatic experience for him." Weener said Rockefeller was cooperative but was "not up to it."
NTSB officials said it is not unusual for those who have survived fatal accidents to be emotional during interviews. Nor is it unusual for the board to allow participants additional time to complete the interview.
Botallico said Rockefeller is cooperating.
"Billy is fully cooperating with the NTSB," Botallico said. "He needed to get some rest. He's very traumatized by the loss of life. It's best that it comes from him what happened. He's a quality human being. I know him personally. I've been a conductor and representative, and I'd be proud to have him as my engineer."
Rockefeller started out as a janitor at Grand Central and "worked his way up," Botallico said.
"He's been in operations for quite a while," he said. "He used to change the time of the trains in Grand Central. He was volunteer fireman. He's just a guy who's always gone out of his way for everyone else. It brings me to tears because the loss of life is something that -- it's the hardest thing to deal with. When you lose life it's difficult for all."
Said Harrod: "This engineer, I'm sure, as the evidence comes out, I think we're really looking at a sad, really basic kind of inattentiveness. Nothing fancy: No alcohol, no drugs, maybe not even a cell phone. Just plain vanilla inattentiveness."
Michael McClendon, who supervised engineer Rockefeller for several years, spoke to CNN affiliate WCBS.
" I wish this didn't happen to anyone, but I sure as hell don't want it to happen to him," he said.
CNN's Allison Malloy, Mike Ahlers and Ross Levitt contributed to this report.
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