A former Sonoma County man who was touted as an example of why California should relax its "three-strikes" sentencing law is back in jail on car theft charges.

Dale Curtis Gaines, 56, was arrested Sunday morning on suspicion of stealing a pickup truck from a Shell gas station in Marin County, Novato police Lt. John McCarthy said.

The owner of the 1995 Ford Ranger left his keys in the ignition when he went into the Novato store, McCarthy said. Gaines got in and drove off, he said.

"This guy happened to be right there looking for a vehicle and he jumped in and took it," McCarthy said.

Gaines was arrested moments later as he drove the pickup south on Highway 101 near Ignacio Boulevard, McCarthy said. He pulled over for officers and surrendered without incident, McCarthy said.

The former Santa Rosa resident, who now lives in Mill Valley, was being held in lieu of $25,000 bail.

Gaines had served 15 years in prison when he was released in March under voter-approved Proposition 36, which relaxed the state's three-strikes law.

Under Prop. 36, anyone sent away for life on a third "strike" that was not serious or violent could receive a new sentence. Gaines, who had been sentenced to 27 years to life in 1997 for possessing stolen computer equipment, was deemed eligible and freed with credit for time already served.

A team of lawyers from Stanford Law School's Three Strikes Project took up Gaines' case, receiving widespread media attention. They argued he was an exception to three-strikes because of his diminished mental capacity.

On Tuesday, Michael Romano, project director and co-author of Prop. 36, said Gaines probably wouldn't have been arrested Sunday if he had received adequate mental health treatment upon release. Unlike other parolees, people freed under Prop. 36 don't get a caseworker or other help, he said.

Romano defended Prop. 36, saying the recidivism rate is well below the state average, which he said was 16 percent. He said statistics on the 991 people released under Prop. 36 would be out next week.

"This is the exception so far," Romano said. "It's more of a special case because he's extremely mentally ill. It goes to show why people leaving prison need the resources that everybody else leaving prison gets."

Three strikes was enacted by voters in 1995 to target repeat offenders such as Richard Allen Davis, who strangled 12-year-old Polly Klaas after kidnapping her from her Petaluma home in 1993.

Critics said it resulted in unfairly harsh sentences for some people who committed relatively minor third offenses.

With November's passage of Prop. 36, about a dozen people in Sonoma, Mendocino and Lake counties were eligible for re-sentencing. The number of those who have been released or re-arrested was not immediately available.