A projectile might have struck the windshield of Amtrak Train 188, just minutes before the train crashed Tuesday night, and investigators said Friday that they had called in the FBI to analyze the damage.

Officials at the National Transportation Safety Board could not say whether engineer Brandon Bostian had been struck or incapacitated by a projectile.

The surprising revelation at a news conference Friday night significantly expands the scope of the crash investigation beyond either mechanical failure or operator responsibility.

Two other trains - a SEPTA commuter train bound for Trenton and an Amtrak Acela arriving from New York - were struck by projectiles in North Philadelphia on Tuesday night shortly before the Amtrak wreck.

An assistant conductor on Amtrak 188 told investigators that three to four minutes out of Philadelphia, she heard a radio conversation between her engineer and the engineer of a nearby SEPTA train, "who reported to a train dispatcher that he had either been hit by a rock or shot at," NTSB board member Robert Sumwalt said Friday.

Sumwalt said the Amtrak assistant conductor, 39, then heard her engineer "say something about his train being struck by something" as well.

"We have seen damage to the left-hand lower portion of Amtrak windshield that we have asked the FBI to come in and look at for us," he added. He said the particular damage appears in a "circular" pattern, emanating outward. The right side of the windshield, as viewed from inside the train, has extensive damage caused by the crash, Sumwalt said.

NTSB investigators interviewed Bostian on Friday, and the engineer was "extremely cooperative" but could not recall what happened in the crash, Sumwalt said.

Investigators are trying to determine why Train 188 suddenly accelerated in the minute before the crash and derailed when it entered a 50-m.p.h. curve traveling more than 100 m.p.h.

Bostian's lawyer has said his client suffered a head wound and a concussion, and has no recollection of the crash. The engineer told investigators on Friday that he did not recall any projectiles and did not report being struck by anything entering his cab.

Previously, Mayor Nutter and SEPTA officials had discounted any connection between those two incidents and the Amtrak wreck, which killed eight people and injured about 200.

The FBI confirmed it was asked Friday to aid the NTSB in investigating particular windshield damage to the train, but said there was no separate federal criminal investigation linked to the derailment.

The engineer of SEPTA Train 769, which was disabled when a projectile broke its cab window, has been asked to speak with NTSB investigators, a SEPTA spokesman said Friday.

The SEPTA train was struck by the unknown projectile about four miles south of where Train 188 derailed. The Amtrak train passed the SEPTA train after the SEPTA train had been hit and was stopped at SEPTA's North Philadelphia station.

Radio conversations involving Bostian and the SEPTA engineer would have been recorded by Amtrak dispatchers, since both trains were on Amtrak-controlled tracks.

Earlier in the day, Bostian had operated a southbound Amtrak train to Washington, which apparently had mechanical problems and arrived 30 minutes late.

Bostian told investigators Friday that he had not felt fatigued or ill before the wreck.

"He expressed no operational problems, any sort of significant problems with the train. . . . He felt good, he felt alert, he said he felt fine, there was no issue," said NTSB spokesman Peter Knudson. "If he would have felt rushed or stressed, that would certainly have" come out.

Investigators are also conducting drug tests. Bostian's lawyer has said the engineer was not using drugs or alcohol.

Bostian and the two assistant conductors told investigators of their memories of the trip before the crash, the derailment, and the chaotic moments afterward. The conductor was injured and remains hospitalized, unable to be questioned, Sumwalt said.

The assistant conductor who overheard the engineers' conversations was in the fourth car, the cafe car, with 15 passengers. She said she felt rumbling and then her car toppled onto its side. She said she and the passengers were unable to get out until emergency responders arrived to rescue them.

She described Bostian as "great to work with" and someone who was "always offering to help her with her job," Sumwalt said. Bostian was a conductor before becoming an engineer.

The second assistant conductor, a 35-year-old man, was in the seventh and last car with 40 passengers, Sumwalt said. That crew member "felt shaking, then two major impacts . . . the interior seats disconnected."

At the crash site Friday, work crews were busy replacing damaged track, power lines, and other equipment to restore service to the heart of the busy Northeast Corridor.

Work is underway to replace 22 track panels along two of the four tracks at the site. Each panel is 60 feet long, Amtrak spokesman Craig Schulz said.

Crews also are installing four new catenary poles - the H-shaped steel structures that hold the overhead wires along the tracks.

He did not have a cost estimate for the work, which also includes testing the signal and power systems. He said crews would continue working around the clock until repairs were complete.

Amtrak officials said they hoped to have trains running again by Tuesday.

Amtrak chief executive Joseph Boardman apologized for the wreck in an online statement, saying, "Amtrak takes full responsibility, and deeply apologizes for our role in this tragic event."

Boardman said Amtrak was "working with the individuals and families affected by this event to help them with transportation, lodging, and of course, medical bills and funeral expenses."

Also Friday, U.S. Rep. Bill Shuster (R., Pa.), chairman of the House Transportation Committee, said he would convene hearings on the accident after Memorial Day.

Emergency responders gathered Friday at City Hall to describe the massive, coordinated response to the crash.

Police and fire officials described calls coming in from passengers unable to say where the train was.

"The people were frantic, but they were also calm," dispatch supervisor Ken Carey said. "They were able to say, 'I've been in an accident, but I don't know where I am.' "

Eight people injured in the derailment remained in critical condition - five at Temple University Hospital (down from six Thursday), two at Aria Health-Torresdale Campus, and one at Penn Presbyterian Medical Center.

Officials have said more than 200 people were injured in the crash, about 150 of whom ended up in hospitals.

At a brief news conference outside the Temple hospital, U.S. Sen. Robert P. Casey (D., Pa.) said he had toured the hospital to get a sense of the challenges facilities faced as victims of the crash poured in.

He said he was "inspired by the really miraculous work that was done here under the most horrific of circumstances."

For more photographs and updates on the derailment, travel and commutes, and survivors' condition, visit Philly.com throughout the day.EndText

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Contributing to this article were Inquirer staff writers Laura McCrystal, Jeff Gammage, Mike Newall, Stacey Burling, Jeremy Roebuck, and Mari A. Schaefer.