By Molly Daly

PHILADELPHIA (CBS) — As the FBI investigates reports that Amtrak train 188’s locomotive was hit by an object just before it went off the rails, the lead NTSB investigator into the crash expressed skepticism that someone fired a shot at the locomotive during an appearance on CBS’s Face the Nation.

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Anchor Bob Schieffer asked the NTSB’s Robert Sumwalt if he thought it possible that someone shot at the train.

“I’d like to downplay that part,” Sumwalt told Schieffer. “I’ve now seen the fracture pattern. It looks like something about the size of a grapefruit, if you will. And it did not even penetrate the entire windshield.”

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As for whether the object hitting the locomotive’s windshield could have distracted the engineer enough to have factored into the crash, Sumwalt would not rule that out.

“Certainly, everything is on the table in that respect,” he said. “We’re really looking at everything, and this is just another piece of the investigation.”

Sumwalt said they’ve asked the FBI provide the agency’s technical assistance to help the NTSB determine exactly what caused that fracture pattern on the windshield.

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And that answer may not come soon. Such investigations can take as long as a year.