PHILADELPHIA — As federal investigators try to find out why an Amtrak train that crashed in Philadelphia sped up in the last minute before it derailed, Amtrak’s top official said the railroad takes full responsibility for the deadly wreck.

Joseph Boardman, Amtrak president and CEO, said in a letter on Amtrak’s official blog Thursday that it is cooperating fully in an investigation into the accident that killed eight people and injured more than 200 this week.

“With truly heavy hearts, we mourn those who died. Their loss leaves holes in the lives of their families and communities,” Boardman wrote. “Amtrak takes full responsibility and deeply apologizes for our role in this tragic event.”

He said the railroad’s goal is “to fully understand what happened and how we can prevent a similar tragedy from occurring in the future.”

Meanwhile, the National Transportation Safety Board said Thursday that in the last minute or so before the derailment, the Washington-to-New York train sped up from 70 mph until it reached more than 100 mph at a sharp bend where the maximum speed is supposed to be 50 mph.