Updated

Both maintenance workers killed by an Amtrak train near Philadelphia last year were on drugs when the crash happened, test results show, but that doesn't appear to have factored into safety lapses and miscommunications being blamed for their deaths.

Toxicology reports released Thursday by federal safety investigators show backhoe operator Joseph Carter Jr. tested positive for cocaine and supervisor Peter Adamovich had morphine, codeine and oxycodone in his system. Tests on train engineer Alexander Hunter, who was injured in the crash, showed evidence of marijuana use.

Other documents released by the National Transportation Safety Board pinned blame on a lax safety culture that put Carter, 61, and Adamovich, 59, in harm's way as they performed maintenance on an active track in April.

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"Although the materials do not reflect that drug use was the cause of this incident, any positive drug test result is completely unacceptable," Amtrak President and CEO Charles "Wick" Moorman wrote in a letter to employees.

Among the other documents released Thursday was a report posted in error — and later removed — in which investigators criticized Amtrak managers for allowing the track maintenance work to go on without a detailed plan identifying safety hazards. NTSB investigators wrote that the railroad's assertion that a plan wasn't needed amounted to "a post-accident circling of the wagons."

Investigators said they determined that the track where Carter and Adamovich were struck was closed to trains until about 20 minutes before the crash, and that a foreman who took charge after a shift change never called to have it closed again.

Hunter, 47, blew the horn and hit the brakes once he saw equipment on an adjacent track and then on his own track, about five seconds before impact. The train slowed from 106 mph to 100 mph and only came to a complete stop about a mile down the track.

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A lawyer representing Carter's family said his positive drug test was irrelevant to the systematic failures the investigative report described at Amtrak.

Carter, Adamovich and Hunter had all passed previous drug tests given as part of their employment, according to the investigative reports. No drugs were detected in post-crash tests given to surviving maintenance workers, the train's conductor and two assistant conductors.

Federal regulators say they've seen an uptick in drug use by rail workers in recent years. Starting in April, workers who perform track maintenance will be subject to the same random drug and alcohol testing as train crew members.

In a statement, the Federal Railroad Administration urged railroads to be vigilant in substance testing and "do all they can to ensure employees are not operating or working under the influence."