AT a little past midnight on a recent Sunday night in a Los Angeles suburb, Bell, the police moved to stop a weekly illegal street race that had been carving up the side streets along the Long Beach Freeway for six months.
Police cruisers arrived and blocked dozens of cars: Acuras, Ford Mustangs and at least one right-hand-drive Honda, imported illegally from Japan and modified for racing. By the time the tire smoke cleared, the police had arrested eight people, impounded 12 cars (five with what the police said were stolen engines or transmissions) and issued dozens of citations.
Participating in the joint operation were officers from 10 Southern California police agencies and one civilian: Mike Bender, one of the country's foremost authorities on auto theft.
He accompanied the mission, as he has many others over the last decade, to help the police identify stolen car parts and to train officers to recognize the connections among street racing, auto theft and insurance fraud.
Mr. Bender, 51, a former special agent for the National Insurance Crime Bureau, acts as a consultant to police departments and conducts auto-theft seminars around the country. His message is that thieves have gone high-tech, so the police need to go high-tech, too. To prove the point and destroy the myth that advanced antitheft systems are impenetrable, Mr. Bender often heads out to his garage to get his hands dirty and crack security systems himself.
The police contact Mr. Bender for help when their cases get technical: for instance, when thieves override the transponder immobilizer systems in most new cars. In these antitheft systems, the vehicle is designed to start only when a chip inside the owner's key sends the proper numeric signal to the vehicle's internal computer. The technology, and attempts to circumvent it, can bewilder longtime theft investigators.
''The poor guy gets a phone call from me every other week,'' said Cpl. Jeff Higbee, an investigator with the Ontario Police Department in California, who participated in the Bell operation. ''And he almost always has the answers.''
In addition to offering help to the police (typically without charge), Mr. Bender holds regular training seminars. One last month near San Diego was entitled, ''Auto Theft in the 21st Century.'' Sixty insurance agents and police investigators from around the country paid $135 each to learn about topics like what to look for when a new security system is bypassed or the techniques thieves are using to alter vehicle identification numbers on stolen vehicles.
The police have traditionally kept such conversations quiet, fearing they could tip off aspiring thieves. Mr. Bender's mission is to bring investigators into the digital age and get them to share information, just as their adversaries are doing on Web sites, message boards and forums like YouTube, where dozens of videos show off car-hacking and street-racing techniques.
''I don't think there is anything we talk about at the seminars that isn't on the Internet, being discussed by the other side,'' Mr. Bender said. ''In the past, we have only been keeping information from ourselves.''
Mr. Bender's rising profile among auto- theft investigators is partly a reaction to changes in the way thieves are stealing cars. In 1991, according to the F.B.I.'s National Crime Information Center, 1.7 million cars were stolen. In its latest report, for 2005, the annual toll fell to 1.2 million, thanks partly, Mr. Bender said, to improving antitheft technology.
But that good news has a dark lining. Fifteen years ago, nearly every stolen automobile was recovered. Young thieves often took cars for joyrides and then abandoned them. Today, according to the F.B.I., only 62 percent of vehicles are recovered. Professional crime rings are stripping cars or shipping them overseas, and antitheft technology is not stopping them. ''There's a reason we're not recovering them,'' Mr. Bender said. ''The bad guys have evolved. They are much more sophisticated.''
At the heart of Mr. Bender's expertise is a curiosity about new technology and a long history battling auto theft. He began his career in the late 1970s as a beat officer and detective in the Los Angeles and Simi Valley police departments, then pursued a childhood interest in cars and migrated to the auto-theft department.
In 1991, after retiring early from the police force, he joined the National Insurance Crime Bureau, a nonprofit industry group devoted to fighting auto theft and insurance fraud. The bureau moved him to Santa Clara, Calif., in Silicon Valley, where he witnessed the arrival of street racing in that community.
In 2003, Mr. Bender left the bureau and started a business, VinTrack, selling high-tech tools to help law enforcement authorities to identify stolen vehicle components. But most of his time is spent offering advice on cases and training the police.
For example, he frequently shows investigators a video he made demonstrating how some electronic control modules can be disabled. The car can then be started without a key that has an embedded transponder. In a variation of the test, Mr. Bender shows how a car's control module can be replaced with another from an older car without a transponder, then started without the proper chip-equipped key.
Mr. Bender's videos and seminars have helped to weaken the aura of infallibility around the transponder. After the technology was widely adopted in the late '90s, many automakers marketed their cars as unstealable. Insurance companies reacted by denying many claims on stolen transponder-protected cars, in the belief that owners who had all their keys after their cars disappeared must be lying about the theft.
Mr. Bender campaigns against that myth.
''I tell every insurance group, you cannot deny a claim based solely on the fact the car had a transponder, no matter how expensive the claim is,'' he said.
He has also enlightened the police about the connections among street racing, auto theft and insurance fraud. Because racers often wreck their cars, or bet and lose valuable aftermarket parts in competition, the number of fraudulent insurance claims often skyrockets with the arrival of illegal street racing in a community.
Sgt. Bob Jagoe of the Baltimore County, Md., police department said he never made those connections when street races began in his county five years ago. Racing appeared to be a relatively contained safety problem. Growing but seemingly trivial reports of stolen tires and engine parts simply did not cross his desk.
In 2002, Sergeant Jagoe attended one of Mr. Bender's seminars at a conference for the International Association of Auto Theft Investigators. One of the techniques he picked up at the seminars was to go after the underground chop shops that retrofit racing cars with stolen parts like exhaust systems, suspension parts and strut bars.
Last month after the operation in Bell, Mr. Bender was circumspect about its success. The fact that the large weekly races existed ''was an affirmation that street racing and auto theft either isn't going away, or that it has come back again,'' he said. ''I guess I'm in no danger of putting myself out of business anytime soon.''