Stunning video is raising questions for people in East Palestine, Ohio, CBS Pittsburgh reports.

The video, which captured the train 20 miles before it reached the site where it derailed, is raising questions about when the crew knew there was a problem.

The video, obtained by the Pittsburgh Post-Gazette, was taken by a security camera at an equipment plant in Salem, Ohio. What appears to be sparks and flames can be seen in the video under one of the train cars as it passes the plant. The National Transportation Safety Board referenced the video at a news conference last week.

“We have obtained two videos which show preliminary indications of mechanical issues on one of the rail car axles,” said Michael Graham, a member of the NTSB.

That second video came from a processing plant in Salem a mile down the track. In front of that plant is a hot box detector, which scans the temperature of the axles as a train passes and sounds an alert if they’re overheated.

“The crew did receive an alarm from a wayside detector shortly before the derailment indicating a mechanical issue,” Graham said. “Then an emergency brake application initiated.”

The NTBS says there was an alert, but it’s not known if it came from the hot box detector in Salem or the next one down the track 20 miles away in East Palestine.

And if the alert wasn’t triggered when the train passed Salem, why not? CBS Pittsburgh asked Scott Wilcox, a retired Norfolk Southern engineer.

“Generally speaking, after the length of the train has passed over the detector, it will tell you there are no problems found,” Scott Wilcox said. 

The NTSB has obtained the train’s data recorder and audio recordings. They’re being analyzed at an NTSB lab in Washington, D.C. The agency is also checking whether all the detectors were working properly.

It’s expected to release its preliminary findings within 30 days.