At 46, Doreen Giuliano reinvented herself. She dyed her hair blond and tanned at a salon. She left her white seven-bedroom, colonial-style house for a spare basement apartment three miles away. She took on a new name, and for about a year, she said, she rode her bicycle around her new neighborhood, trying to attract the gaze of a young man whom she badly wanted to get close to.

This was no midlife crisis, though. It was a one-woman sting operation.

Ms. Giuliano is the mother of John Giuca, a Brooklyn man who was convicted three years ago along with another man in the 2003 killing of Mark Fisher, a college student from New Jersey who was found beaten and shot five times after a night out in New York City. Ms. Giuliano claims her son is innocent and has mounted an unstinting campaign to free him from prison, where he is serving 25 years to life. She maintains a Web site to rally supporters of her son, and Mr. Giuca’s lawyers have filed an appeal alleging prosecutorial misconduct.

But in the last two years, Ms. Giuliano’s activism reached dramatic new heights. Having assumed the role of a 30-year-old research analyst from California who wore six-inch heels and push-up bras, she set out to meet a man named Jason Allo, a contractor who lived in Bensonhurst, Brooklyn. He was a juror in her son’s trial.

It is unclear why Ms. Giuliano took aim at Mr. Allo, though she said in an interview that she followed two other jurors before him. She rented an apartment near Mr. Allo’s house and said she followed him for months. After they finally met one day in October 2007  she almost ran down Mr. Allo and a friend on her bicycle  Mr. Allo handed the newcomer his phone number. He did not recognize her, though she had been a constant presence at her son’s trial.