good evening i am elizabeth elizabeth cook. >> and bart has opened an investigation. >> reporter: a woman witnessed the entire thing here in san bruno. the man was harmless in the video. the bart officer tasked tas tased him for no reason. the man was harassing riders and was convinced to talk to him on the platform. witnesses can be heard saying he did nothing wrong the officer tases the man and he is dragged to the aisle. >> don't move or i will tase you again. taser, taser. >> reporter: 5 full seconds. one witness was so horrified she wrote a blog post and reported it to bart police n . in a statement to kpix5 bart is launching an investigation and an audit for part police. >> reporter: he was booked for public intoxication and parole violation. >> the bart police have a taser policy. they can use a taser if the suspect poses an immediate threat to their life or another person's life. >>> the oakland police department, we have the real story at the headquarters. >> reporter: thomas frazier was hand picked to fix the oakland police department. the fixer couldn't figure it out and got ca