Emergency personnel work at the scene of an Amtrak train wreck on May 12, 2015, in Philadelphia.
Joseph Kaczmarek—AP
June 2, 2015 11:23 AM EDT

The National Transportation Safety Board’s investigation of last month’s deadly Amtrak crash outside Philadelphia is zeroing in on the engineer’s cell phone records after establishing that there were no mechanical problems that contributed to the accident.

According to a preliminary report released Tuesday, the NTSB has established that there were “no anomalies” in the train’s brake system, signals or track structure. Investigators have obtained engineer Brandon Bostian’s cell phone records and have established that calls and texts were made that day, but they’re still working to figure out whether he was on his phone as he was driving the train. Bostian suffered a head injury in the crash, and his lawyer has said he has no memory of what happened.

The NTSB also found damage to the train’s windshield, but couldn’t determine whether this came from rocks that were thrown at the train or from the crash itself. They found no evidence that the damage was caused by gunshots.

Write to Charlotte Alter at charlotte.alter@time.com.

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