By Mark Abrams

PHILADELPHIA (CBS) — Federal investigators are preparing to release thousands of pages of documents and evidence related to the probe of the deadly derailment of Amtrak train 188 in May.

Eight people died and more than 200 were hurt in the derailment near the Frankford Junction.

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Among the key evidence, the National Transportation Board is prepared to release is a transcript of the interview with the train engineer, 32-year-old Brandon Bostian.

The documents are expected to be released at 1 p.m.

On May 15, federal authorities interviewed Bostian, and NTSB board member Robert Zumwalt talked about what they learned.

“Our investigators found the engineer to be extremely cooperative,” he said. “He was accompanied by his lawyer, which is not at all unusual. And the engineer encouraged us to contact him further, again, contact him again, if we needed anything else.”

But Zumwalt conceded Bostian was unable to shed any light on why the train was traveling at 106 miles an hour going into the curve at the junction.

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He said the engineer had no recollection of the accident – only ringing his warning bell as he came through North Philadelphia.

The FBI also was called to investigate evidence that a rock or some other projectile, such as a gunshot, hit the windshield of the engine just before the derailment.

Authorities conceded there was evidence something struck the window, but didn’t speculate on whether that had any bearing on the crash.

The documents being released will be used by the NTSB to reach some conclusions on what may have caused the derailment.

A final report is not expected until spring.

The Philadelphia Police Department criminal investigation is also underway.

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These findings, along with NTSB evidence gathered by detectives, are all expected to be forwarded to the District Attorney at some point,  who will then decide if any criminal charges might be filed.