According to the San Francisco Police Department, the attempted kidnapping occurred close to 9 p.m. on the 2800 block of Steiner Street between Green and Vallejo streets.
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Police say a 31-year-old female victim was walking on the sidewalk when the suspect got out of his car and tried to grab her. The suspect is described as a man in his 30s.
The witness saw the incident and jumped in, which caused the suspect flee.
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The suspect was arrested shortly thereafter.