BALTIMORE — The school bus driver who was killed along with five others after he drove into a transit bus was not authorized to drive a school bus at the time, The Baltimore Sun reports.

A letter from the Maryland Motor Vehicle Administration (MVA) notified Glenn Chappell in early September that he was “no longer authorized” to drive a school bus and could lose his license unless he provided documentation that a doctor had cleared him to drive, according to the newspaper. However, the MVA hadn’t informed the school system that Chappell had lost his driving privileges, and he continued to transport 17 special-needs and homeless students. The state did not revoke Chappell’s CDL until the day after the crash, and that is when school officials learned of the revocation, The Baltimore Sun reports.

Chappell had let his commercial driving privileges lapse for failing to show proof of sound health before, according to the newspaper. In 2015, he failed to provide renewed certification until one month after his license expired.

Meanwhile, investigators are looking into whether a medical event caused the crash, after ruling out mechanical failure and finding no reason to suspect Chappell intentionally caused the accident. In 2014, he crashed his car into a guardrail, and his wife told police he was taking medication for seizures, according to The Baltimore Sun.

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