A Wilton man, acting on what he says was instinct, chased and nabbed a suspected purse-snatcher in Norwalk earlier this week. While near a CVS store in Norwalk Tuesday, a woman told 61-year-old Frank Costanzo her purse had been stolen. After seeing the suspect, Costanzo gave chase on a bicycle over railroad tracks, across a bridge and into a nearby condominium complex. He then, along with two other men, grabbed and held the suspect until police arrived.Norwalk police have not released an official report on the incident, which is still under investigation. The woman whose purse was stolen has thanked Costanzo, who says he still doesn't know her name. Costanzo insists he did the same thing anyone else would do. He also says he prays for the young suspect and hopes he can get help.