On the night of August 17, 2007, Virginia Lopez was working at a restaurant in Julian, California, near San Diego. While working, she had three shots of tequila between 8:45 p.m. and 10:15 p.m. At about 11:00 p.m., she left work to drive home.

As she drove home, she ran head-on into a pick-up driven by Allan Wolowsky, killing him. About two hours after the accident, Ms. Lopez provided a blood sample.

Jorge Peña of the San Diego County Sheriff’s Regional Crime Laboratory analyzed Ms. Lopez’s blood, which he measured with a gas chromotograph as having a .09 % blood-alcohol concentration (BAC).