(NBC News) As investigators continue to search for answers in the tragic bus crash injuring 24 children in Chattanooga, Tennessee, authorities reported on Wednesday that a sixth child has passed away.

The National Transportation Safety Board also relayed that the bus was not on a route approved for transporting children at the time of the crash.

"That's one of the things we're exploring is as has he done it before and b if so why?" said NTSB Chairman Christopher Hart.

Chattanooga Police also revealed that the driver's toxicology report showed no signs of drugs or alcohol in the driver's system at the time of the crash.

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