In 2006, Shawna Matthews was a single, unemployed mother living in public housing when a man she knew only by a nickname offered her $700 to buy a gun for him.

Matthews took his money and walked into a South Philadelphia gun store. She chose a .40-caliber Smith & Wesson pistol, though she knew nothing about firearms.

"He was a big guy, so I just picked out a big gun," she said in an interview last week.

The next year, Matthews was indicted in federal court for making a "straw" purchase - buying a firearm for someone who cannot legally own a gun.

Straw buyers are a leading source of illegal guns on the streets, and often they are women with clean records working at the behest of boyfriends and acquaintances.

"From my experience, women tend to commit this crime for either love or money, and it's not a very good trade either way," Assistant U.S. Attorney Bea Witzleben said.

The charge carries a five-year maximum sentence, and Matthews, 30, was facing several months in prison.

But when she pleaded guilty, U.S. District Court Judge Anita B. Brody saw an opportunity. She was tired of the parade of women in her courtroom who had made straw purchases without giving thought to the idea that they were arming criminals and breaking the law.

"It got to the point where I felt I had to do more than put somebody in prison," the judge said.

Brody told Matthews to think of a way to spread the word to young women about the consequences of straw buying.

At her sentencing this summer, Matthews said she would be willing to speak out, and she eventually suggested the Job Corps program as a place where she could address young inner-city women.

Last month, Brody, Witzleben, and Cathy Henry, Matthews' public defender, accompanied her to a "female enrichment" gathering at the Job Corps campus in South Philadelphia.

All four women warned the group about the dangers of straw purchasing, but Matthews' story seemed to have the biggest impact.

"I have to tell you, you could hear a pin drop in the room when she started talking," Witzleben said. "You could tell when we were talking to them, some of them may have already done it or had been approached to do it."

Immediately after the presentation, one woman in attendance told a Job Corps staff member that she was planning to buy a gun that weekend for a friend, who assured her she wouldn't get into trouble.

The woman said that she needed the money, but that Matthews had persuaded her not to do it.

"If the judge had put Shawna Matthews in jail for five years, that woman would have bought a gun," Henry said.

Matthews said another woman came up to her after the event and started asking questions. She could tell the woman "was in that situation," but was afraid to admit it.

"Don't do it," she told her. "It's not worth it."

Bernice Lecoin, a Job Corps staff member who organizes the female enrichment group, said many of the students "didn't even know what the term straw purchasing was."

"When Shawna opened up, you could hear it. The audience was like, 'What?' " she said.

Several students described the event as eye-opening.

"The fact is that you could be doing something that you think is so innocent, and it could spiral out of control," said Nikita Joseph, a Job Corps student.

Matthews said she was naive when she bought the gun.

"Now that I think about it, I say, 'Why couldn't he get it himself?' " she said. "At the time, it was just $700."

Matthews plans to fulfill her required 50 hours of community service by continuing to speak to groups of women. She also received six months of house arrest and five years of probation.

She remains a single mother of four children and, with a felony conviction on her record, has struggled to find work.

The man for whom she bought the gun, Alonzo Wallace, was arrested by Philadelphia police while carrying the weapon. He was charged with being a convicted felon in possession of a firearm. His case is pending in federal court.

The ATF traced the weapon back to Matthews and she promptly confessed.

"My first question was, 'Did he do something with that gun?' " she said.

Luckily for her, the gun was not used in a crime.

Brody said she had never taken such an unconventional approach with a defendant, but she felt that deterrence - a factor considered in any sentence - was not being properly addressed in straw-purchasing cases.

"Deterrence also means putting the word out on the street," Brody said. "I wasn't worried about this particular defendant doing something like this again."

U.S. District Judge Harvey Bartle 3d, the chief judge for the Eastern District of Pennsylvania, supported Brody's idea.

"How do you get the message out into the community about what you're doing in the courtroom?" he asked. "When you can go . . . deliver that message personally, they hear you."