WILLOWS, Calif. (AP) – Authorities have released the cause of death for nine of the victims of a Northern California crash a charter bus full of students and a FedEx tractor-trailer.

The Glenn County Sheriff-Coroner’s office said Monday that seven of the victims in April’s crash succumbed from asphyxiation due to smoke inhalation. The other two died of multiple traumas from the collision.

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Sheriff Larry Jones said a tenth victim died in a Sacramento County hospital burn unit.

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The bus was carrying 44 students from Southern California for a free tour of Humboldt State University on the state’s far north coast. Many were hoping to be the first in their families to attend college. Five students and three adult chaperones died, along with the drivers.

The cause of the crash was under investigation.

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Copyright 2014 The Associated Press.