“It was the crying that really got to me,” he said.

He gave her $37 and hugged her goodbye, imagining her purchasing a ticket and boarding a westbound train to some city where a loving mother would welcome her home and dry her eyes.

Image Residents of Davis, Calif., have circulated this flier of the young woman they call the Crying Girl. Credit... Max Whittaker for The New York Times

Two weeks later, he saw the same girl. Still crying.

“I’m not the vengeful type, but I was angry,” Mr. Baadkar said.

Bernie Goldsmith, a former Wall Street lawyer who moved home to Davis last year, said he was approached by the Crying Girl in March with the same story, tears once again pooling in her eyes. But he was not fooled.

Mr. Goldsmith, 27, called the police but says he got no response. So he decided to post a description of the Crying Girl and the details of her scheme to Daviswiki, a local Web site that allows residents to post and curate geographically specific information on topics as varied as historic buildings, multicultural poetry nights and Davis trivia.

Soon, dozens of amateur sleuths had posted information about her, including a license plate number for her getaway car, a photograph of her in a red sweatshirt, meticulous details about encounters with her, links to her supposed Facebook and MySpace profiles, a flier warning of her swindle and information about how to file a police report.