LOS ANGELES — Prosecutors said Tuesday they will not press charges against former US commerce secretary John Bryson over a series of car crashes blamed on a seizure, which led to his resignation.

The Los Angeles County District Attorney's office said there was insufficient evidence to prove either driving under the influence or hit and run charges over the June 9 crashes.

"Both treating doctors agree that (the) suspect was suffering from confusion following a seizure and crashed as a result," it said in a charge evaluation sheet.

"Based on doctors' opinions, there is insufficient evidence to show knowing failure to provide personal information for hit and run. Further, based on blood test and medical condition there is insufficient evidence to prove driving under the influence," it added.

The blood tests proved negative for alcohol and other controlled substances, but positive for Ambien, a drug used to treat insomnia, it said. "Quantitative analysis for Ambien showed low end of therapeutic levels. Criminalist cannot say it was a factor in driving or the collisions."

Bryson, 68, has been under a felony investigation in California over the two hit-and-run incidents.

According to an account of events from the Los Angeles County Sheriff's Department on the day of the crashes, Bryson's Lexus rear-ended another car as it waited at a railway crossing in the city of San Gabriel.

Bryson then spoke to three men in the damaged car and drove away, but hit their Buick again in the process. He then drove to the city of Rosemead, where he struck a second car.

The secretary later was found "alone and unconscious behind the wheel of his vehicle," said officials.

Neither alcohol nor drugs were suspected as being factors in the accidents, and no one was injured, but Bryson took a medical leave of absence afterward, before announcing his resignation on June 21.