HE Sony Clié was as good a smoking gun as investigators could get in a white-collar crime.

When the police in San Jose, Calif., broke up an identity-theft crime ring two weeks ago, they used search warrants to seize and examine the hand-held organizers of the suspects, including that of the man the police said had been the ringleader, Julian Torres, 21.

Stored on Mr. Torres's Clié, investigators said, were the names of more than 20 victims along with their Social Security, bank account and credit card numbers and other personal information. Mr. Torres's To-Do list included tasks like picking up materials at the local office supply store to make fake checks, the police said. E-mail messages contained confirmations of transfers from victims' bank accounts. He had even used the Clié's digital camera to take pictures of his partners in crime. It was hard for Mr. Torres to deny the Clié was his, the police said, given that he had entered his parents' phone numbers under "Dad" and "Mom."

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"This was the tool he used to perpetrate his crimes," said Alan Lee, a detective from the San Jose high-tech-crime unit who helped on the case. "Everything is there." Information on the Clié helped investigators find another two of Mr. Torres's accomplices, he said. Mr. Torres is being held in jail on $1 million bail.

As hand-held organizers like the Clié and Palm have soared in popularity, it's not just law-abiding citizens who appreciate their usefulness in managing appointments, contacts and schedules. Criminals, too, are using them to coordinate their activities. And the rise of the organizer as a criminal tool has bred a new category of forensic scientist: the Palm reader.

Drug dealers use contact lists to track buyers and suppliers, investigators say, while drug makers, like those who run clandestine methamphetamine laboratories, use memos to keep recipes and ingredient lists. Pimps use the devices to keep track of clients, revenues and expenses. Smugglers and money launderers track their transactions on spreadsheets. Stalkers have been known to store their fantasies and victims' schedules on their Palms.

Even spies have used them. Corporate spies have downloaded sensitive documents to their hand-helds and quietly walked off with them. Robert P. Hanssen, the F.B.I. agent who was sentenced to life in prison in May for selling secrets to Moscow, used his Palm III to keep track of his schedule to pass information to his Russian contacts. (He also asked them for an upgrade to a Palm VII because of its wireless capabilities.)

Police officials are beginning to seize and analyze personal digital devices in their investigations (a warrant allowing search of a suspect's electronic devices is usually required). What they often find is a trove of detailed, intimate, up-to-date information. That data has been used to prosecute criminals, penetrate their networks and better understand their methods.

The data contained in a hand-held says a lot about its owner, whether that person is a corporate tycoon or a petty thief. "It's an alter ego," said Larry Leibrock, who teaches at the University of Texas at Austin and has been a consultant in many forensic cases involving hand-helds. "It represents their aspirations, who their contacts are, where they spend their time, their tasks and objectives, and how they completed those."

Even sensitive information is rarely password protected, demonstrating a general naïveté that many people have about the security of their digital devices.

Hand-held users often believe - wrongly, investigators say - that what is personal is also private. "People assume that only they can have access," Dr. Leibrock said.

As the criminals are discovering, that isn't the case. The simplicity of a hand-held makes information easily retrievable - not only by the owner, but by whoever has physical access to the device.

"The natural consequence of the information revolution is that our lives are centered around processes and equipment whose sole purpose is to collect data," said David Aucsmith, a security architect for Microsoft. "These devices are all trying to make your life easier.''

While hand-held forensics has mostly been focused on criminal investigations, the devices are popping up as evidence in civil cases as well - in intellectual property disputes between companies, for example, and divorces. A handful of companies, like Guidance Software, the Paraben Corporation and AtStake, have made a business of helping investigators preserve and analyze data.