A good Samaritan called San Francisco cops when she overheard a man on Muni talk about how he had just stolen a cellphone.
That led to the arrest of the 20-year-old man Wednesday night.
The incident was reported around 9:40 p.m. in the area of Stonestown Galleria Mall.
The crook snatched an iPhone from a 24-year-old woman who was sitting on a bench, police said.
When an unidentified citizen heard him talking on a bus about the theft, she called police, who arrested the man. The victim was later identified in a cold show and booked for the theft, police said.