No one noticed her when she was robbing banks. Now, millions have seen her on surveillance videotape, calmly talking on her cell phone during one of the holdups.

Still, no one can say who she is.

The young woman who calmly held up four Northern Virginia banks in recent weeks -- without ever putting down her phone -- remained at large yesterday despite remarkably clear photos of her in robbery action that were broadcast on television and published in newspapers across the country.

Theories abounded yesterday as to who she is, where she might be and why she does it with a phone stuck to her ear. Is she a master of disguise? Is she merely there to rob and then leave -- a tourist bandit? Is she under someone else's control? Is she hypnotized?

Experts yesterday tended to doubt most of the speculation, and they expect an imminent arrest. They also said that the crime can be addictive -- if not also caused by addiction -- and that the cell phone bandit probably will strike again, heavy publicity or not.

Police believe the same dark-haired young woman in her twenties robbed banks in Vienna, Manassas, Springfield and Ashburn from Oct. 12 to Nov. 4. Each time, she showed a note demanding money from a teller. In the last holdup, she also showed the teller a gun.

And each time, she conducted her entire transaction while talking on the phone, appearing indifferent to the whole "I'm committing another federal felony" matter.

Her technique is not entirely new.

In the late 1980s, a gang of bank robbers in the Los Angeles area chatted on cell phones while they waited in line, according to retired FBI agent William J. Rehder. And, back then, cell phones were big and unwieldy.

The gang leader would always give his accomplices a cell phone to keep them pacified, and he would be on the other end of the line, Rehder said. It was a way to reduce nervousness and anxiety -- and to look like a regular customer, he said.

Rehder theorized that Northern Virginia's bank robber -- believed to be about 5 feet 2 to 5 feet 6 and about 120 to 130 pounds -- was using her phone the same way, to look inconspicuous and reduce her anxiety.

Unlike in the movies, bank robbers don't usually have lookouts, getaway drivers and evil overlords, said Rehder, who investigated bank robberies for 32 years for the FBI and is now a security consultant.

Chris McGoey, another consultant in California, said he thought the cell phone "could be a prop to make the cashier think she has backup outside."

But in reality, McGoey said, she's probably talking to a boyfriend, who could be waiting in a getaway car.

Once she's caught, though, the phone shtick could come in handy for her lawyer, McGoey said.

"I can visualize the defense already," McGoey said. "The real crook threatened to kill her or her family if she didn't rob these banks, and she was forced to keep the real crook on the cell phone to track the transaction."

Rehder and Fred Desroches, a sociology professor at the University of Waterloo in Ontario, said bank robbers tell them that stickups can be addictive.

"They said the sensation of walking out of a bank after a successful robbery is very akin to the high you get from a narcotic," Rehder said.

Jon Gould, acting director of the Administration of Justice program at George Mason University, said the cell phone bandit's reluctance to don a disguise showed "audacity that is quite impressive. Either audacity or stupidity."

Two of the most successful bank robbers of all time, the Trench Coat Robbers, robbed banks across the country for 15 years and committed the largest single bank holdup in U.S. history in 1997, the year they were finally caught: $4.4 million from a single branch in Tacoma, Wash. Two reasons for their success: They did not commit robberies near their home town of Kansas City, Mo., and they wore disguises (and trench coats).

The cell phone bandit's calm demeanor led some to theorize she was under someone's spell. Gould said, however: "She's not hypnotized. You can't hypnotize over the phone."

More likely, Rehder said, she is addicted to something and needs money to pay for it, though her clean appearance doesn't shout "drug addict."

Rehder said that more than 80 percent of one robber/one teller holdups are committed by addicts and that such holdups net only about $1,000 or $2,000. Northern Virginia police would not say how much money the cell phone bandit got in each holdup.

"She obviously has a need for cash on a regular basis," which could also come from financial hardship, said Rehder, although he said such cases are fewer.

After her photo appeared on national and local television shows yesterday, experts were surprised she wasn't quickly arrested. "I would put money on the fact that she's caught within a week," Gould said.

Fairfax County police said they had received only six tips by yesterday evening. "She may not be somebody that's local," said police spokeswoman Mary Ann Jennings, "or she may not have a very long history in our area."

Loudoun County sheriff's officials, who first released video of the county's holdup last week, said they had received several calls. "With the amount of attention she's getting," spokesman Kraig Troxell said, "somebody will recognize her."

And, perhaps, that person will call police on a cell phone.

Police say this woman robbed four Northern Virginia banks.