"I'm not a rocket scientist," he insisted, in a spare moment on the job as a Gilroy reserve officer. "How I got in labs for years, I don't know."

Today, Charnota does both, splitting his time between his computer forensics firm, Blackbag Technologies Inc., and patrolling Gilroy streets for free, one of the department's six reserve officers. In a windowless office in Santa Clara, he sniffs out hackers, perverts, identity thieves, tracing crime through electronic circuits; on Gilroy's streets, he directs traffic astride a motorcycle, and storms into danger with the Special Operations Group, Gilroy's SWAT team.

"The computer stuff he does is way above my head," said Sgt. John Sheedy, who first met Charnota in 1992 at age 15, when he joined the Gilroy Police Explorers, a youth leadership program. Sheedy was impressed with him from the start. Tapping a datebook, Sheedy added, "This is my idea of a Palm Pilot."

Charnota had barely touched computers before college, when he wandered into a Fry's Electronics store and "started tinkering." He surfed the Web and clicked into forums where pirated software was resold, driven by an investigator's zeal. It was just a hobby, he said - a hobby he idly mentioned when applying for a security-guard gig at a Silicon Valley computer company, a job where he could do homework on the clock. His interviewer stared at him, and called in the manager.

The good news: Charnota was hired. The bad news: He never got a chance to do that homework. Charnota had been tapped to foil software piracy.

"He's a naturally curious person, and self-taught, which is amazing," said Paul Jordan, who knew him as a childhood friend in Wisconsin, and co-founded BlackBag with him and Derrick Donnelly in 2000.

Hard drives don't lie, Charnota repeats - BlackBag's motto. He's combed the files of a missing man, harvesting clues; he's unlocked a grisly murder case by searching the widower's PC. (Saved in his files: Maps of a lake, complete with weather reports and tide tables, which led detectives straight to his wife's body.) As the secretary of Silicon Valley's chapter of the International High Technology Crime Investigation Association, he keeps tabs on rapidly evolving technologies; every week, he logs 50 to 60 hours behind his desk, sometimes more when he's tracking down child solicitors online.

"I can't sit back and twiddle my thumbs when these kind of cases come up," said Charnota.

No one would blame Charnota if he kicked back after long hours at the keyboard. Instead, he spends another 5 to 10 hours policing Gilroy - at no charge. Reserve officers undergo the same training as full-time officers, take the same calls, but don't get paid, said Sgt. Jim Gillio. The department's reserves put in more than 1,000 volunteer hours last year.

"I don't know how he does it," Jordan said. "He doesn't even drink much caffeine."

Charnota is relieved to get away from the BlackBag office, to interface with people instead of motherboards. Sheedy says he only wishes Charnota could make his two worlds one.

"If there's one regret that I have," he said, "it's that he's not working as a full-time officer."

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