San Bernardino County Sheriff’s Department detectives say Joshua Smith of Hesperia was on a prescription drug that caused him to lose consciousness before the May 11 collision.
The case has been sent to the district attorney for possible prosecution.
Investigators say Smith was behind the wheel of a delivery van when he crashed into a Honda sedan that had stopped at a stop sign at Main Street and Balsam Avenue.
Angelica Garcia, her boyfriend Gerardo Jimenez, and their three children, aged 2, 3 and 9 years old, were all killed.
The family of five was on its way to Disneyland to celebrate a daughter’s birthday when the crash occurred.
The driver of the van escaped with minor injuries.