Southern California authorities say tests show a 30-year-old driver had prescription drugs in his system when his van crashed into a sedan, killing five members of a family heading to Disneyland.

The San Bernardino County Sheriff's Department said Monday that investigators believe Joshua Smith lost consciousness just prior to leaving the roadway and causing the collision on May 11.

The family's sedan was at a stop sign when the van hit and landed on top of it.

Investigators believe the crash was caused because Smith was driving under the influence. Prosecutors will consider whether to file charges.

Two adults and three children were killed. The family was heading from Hesperia, a desert town east of Los Angeles, to celebrate a girl's fourth birthday.

A telephone listing for Smith was disconnected.