Emergency workers look through the remains of a derailed Amtrak train in Philadelphia. (Lucas Jackson/Reuters)

Federal investigators said Wednesday that the engineer of Amtrak #188 did not make a radio transmission saying the train had been struck by something, as one of his crew members said.

Shortly after last week’s deadly derailment, an assistant conductor on Amtrak #188 described an intriguing bit of radio traffic between her train’s engineer, Brandon Bostian, and the operator of a regional commuter train.

The assistant Amtrak conductor told investigators that she heard the Southeastern Pennsylvania Transportation Authority engineer say his train had been hit by a projectile. She also said she thought she heard Bostian say his train was hit by something too.

That latter assertion quickly became part of the National Transportation Safety Board’s investigation into the cause of the crash.

But NTSB investigators have determined that Bostian radioed no such thing.

Emergency personnel work the scene of the deadly derailment in Philadelphia. (Joseph Kaczmarek/AP)

When they listened to a recording of the transmissions, investigators indeed heard the SEPTA engineer describe his train being hit. But “we don’t find that second part. . .There was no transmission from the Amtrak engineer saying, ‘We were struck,’” NTSB spokesman Peter Knudson said Wednesday.

Knudson says it’s still an “open question” whether the Amtrak train was hit by something before the derailment. An FBI technical team analyzed a cracked patch of windshield glass, which had caught the attention of NTSB investigators in part because of its circular pattern, and determined “conclusively” that the damage was not caused by a firearm. Investigators also last week found no evidence in video footage, taken from the engineer’s perspective, that anything hit the windshield, the NTSB said, though they continued to examine that and other evidence.

A SEPTA spokesman said they’re still investigating the circumstances of the projectile that hit their train.

“Our engineer noticed a trespasser in the track area. Not long after that, a projectile of some type hit the train,” SEPTA spokesman Andrew Busch said Wednesday. They have not found the projectile, Busch added. “We’re not sure if it was a rock or something else. That’s still being looked at.”

Busch said “it’s not the most unusual thing” for an engineer to see his train hit. “Unfortunately it’s not necessarily a rare occurrence,” he said, adding that they estimate two or three such incidents a month in their system.

The NTSB interviewed the SEPTA engineer, who stopped his train after it was struck.

“The SEPTA engineer said that the Amtrak engineer announced on the radio, ‘hot track rail two,’ to let him know that the Amtrak train was about to pass the stopped SEPTA train,” according to the NTSB, which released an update of its investigation Wednesday. “He saw Amtrak 188 pass on track 2 and did not notice anything unusual.”

Amtrak #188 then headed on toward Frankford Junction, traveling at twice the speed limit as it entered a sharp curve and derailed, killing eight and injuring more than 200.

The NTSB also said it is analyzing Bostian’s cell phone records, a routine step in such investigations.

Although the records appear to indicate that calls were made, text messages sent, and data used on the day of the crash, the NTSB said, investigators have not yet determined whether there was any phone activity while the train was being operated. To make that determination, investigators have begun to correlate time stamp information from the cell phone with other data sources, the agency said.

Bostian has said his phone was turned off and left in a bag, per policy.