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WASHINGTON — The engineer driving an Amtrak train wasn't using his cellphone just before the train derailed in Philadelphia last month, safety investigators said Wednesday, deepening the mystery of what caused the accident that killed eight and injured about 200.

Tuesday on the NewsHour, security lapses at airport checkpoints put the effectiveness of TSA in question. Also: Former House Speaker Dennis Hastert pleads not guilty to fraud charges, fighting the Islamic State in Iraq, migrants detained in Libya, how marijuana…