It was proven- I think they either contacted her doctors, found her pill bottles, or got her medical records, but they know she was abusing prescription painkillers. I'd have to look up the case to tell you what drugs specifically. IIRC Vicodin was one of them.
From this article: Barreto insisted that she hadn't been drinking the day of the crash. But police said she admitted to taking at least 10 painkillers and muscle relaxants.
http://www.sfgate.com/bayarea/artic...-tragedy-relying-on-future-2718103.php#page-3
And this:
Equally vexing to Pack was the matter of the health care systems role in the accident. Through the police investigation, he came to find out that Barreto was stoned on prescription drugs chased by vodka. She told investigators she had fallen asleep at the wheel.
Police determined that she had been working the health care system for several years, scoring thousands of pills, all through Kaiser doctors. In the two weeks before the accident, she had doctor shopped half a dozen Kaiser physicians in the area to score 340 pain killers and half again as many muscle relaxers. She took them all before the accident.
http://www.38istoolate.com/stories/troy-pack/
This one has more detail: After locating Barreto, investigators discovered she'd been downing vodka and had taken more than a dozen painkillers before the accident. She'd visited multiple doctors in the same Walnut Creek Hospital to get multiple prescriptions for Vicodin and Flexeril, a muscle relaxant.
Outraged by how freely doctors had prescribed the narcotics, Pack founded the Troy and Alana Pack Foundation to work with politicians, police and advocacy groups for tougher public safety legislation, began anti-drunk driving efforts in schools, and fought district attorneys to change the charges against Barreto from vehicular manslaughter to second-degree murder.
Jim Doliber, whose children Hunter and McKenna survived the accident, said he's constantly amazed by Pack's patience, selflessness and resolve.
"I would get angry, but Bob would never get angry," Doliber said. "He focused on what he could do ... He'd just say, 'Well that door is closed, I'll find another.'"
In 2005, a jury convicted Barreto of murder, and the former nanny was sentenced to 30 years to life.
http://www.mercurynews.com/breaking...ter-death-his-children-danville-man-tenacious