Stephen Kovacsics of American Citizen Services, an office of the U.S. Consulate, spoke to a victim who had lost $200,000.

Kovacsics says he is awakened several nights a week by Americans pleading for help with an emergency, such as a fiancee (whom they have only met in an online chat room) locked up in a Nigerian jail. He has to tell them that there is probably no fiancee, no emergency.

Kovacsics said victims can't believe that a scammer would spend months of internet chat just to net $700 or $1,000, not realizing that is big money in Nigeria and fraudsters will have many scams running at the same time.

By 2003, Shepherd was fleecing 25 to 40 victims a month, Samuel said. Samuel never got the 20%, but still made a minimum of $900 a month, three times the average income here. At times, he made $6,000 to $7,000 a month.

Samuel said Shepherd employs seven Nigerians in America, including one in the San Francisco Bay Area, to spy on maghas and threaten any who get cold feet. If a big deal is going off track, he calls in all seven.

"They're all graduates and very smart," Samuel said. "Four of them are graduates in psychology here in Nigeria. If the white guy is getting suspicious, he'll call them all in and say, 'Can you finish this off for me?'

"They'll try to scare you that you're not going to get out of it. Or you're going to be arrested and you will face trial in Nigeria. They'll say: 'We know you were at Wal-Mart yesterday. We know the D.A. He's our friend.' "

"They'll tell you that you are in too deep — you either complete it or you'll be killed."

Samuel said his mother, widowed when he was 16, was devastated when she saw him in the street with Shepherd and realized what he was up to.

"She tried to force me to stop, but the more force she applied, the more hardened I became. I said: 'You can't give me what I want. I want a good life.' "

But Samuel began having second thoughts when a friend was arrested after ripping off a boss for $17,000.

The friend was badly beaten before disappearing into the depths of the labyrinthine Nigerian justice system. Samuel thought of his mother and how she would be left alone if something happened to him.

When he gave up cyber crime at the end of last year, he said nothing to his mother. But she noticed.

"She said she was happy and she could sleep well," he said. "Actually, I started crying. I couldn't control myself. I realized there was more to life than chasing money."

Now when he sees Shepherd in the streets, his former boss just grins.

"He says: 'Don't worry. You'll come back to me.' "

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The many forms of 419 scams

Advance-fee frauds, also known as 419, appear to offer a once-in-a-lifetime opportunity to get rich or find the girl of your dreams. The scams can involve phony websites, forged documents and Nigerians in America posing as government officials. Here are some of the most popular:

•  The "next of kin" scam, tempting you to claim an inheritance of millions of dollars in a Nigerian bank belonging to a long-lost relative, then collecting money for various bank and transfer fees.

•  The "laundering crooked money" scam, in which you are promised a large commission on a multibillion-dollar fortune, persuaded to open an account, contribute funds and sometimes even travel to Nigeria.

•  The "Nigerian National Petroleum Co." scam, in which the scammer offers cheap crude oil, then demands money for commissions and bribes.

•  The "overpayment" scam, in which fraudsters send a bank check overpaying for a car or other goods by many thousands of dollars, persuading the victim to transfer the difference back to Nigeria.

•  The "job offer you can't refuse" scam, in which an "oil company" offers a job with an overly attractive salary and conditions (in one example, $180,000 a year and $300 per hour for overtime) and extracts money for visas, permits and other fees.

•  The "winning ticket in a lottery you never entered" scam — including, lately, the State Department's green card lottery.

•  The "gorgeous person in trouble" scam, in which scammers in chat rooms and on Christian dating sites pose as beautiful American or Nigerian women, luring lonely men into Internet intimacy over weeks or months then asking them to send money to get them out of trouble.