Yeiner Garizabalo, 24, was arrested on misdemeanor charges when the incident happened last month, but he had to be released after 48 hours because there was not enough evidence to hold him.
But now the District Attorney's office has this video and is likely to use it in the case against him.
A BART agent recorded the video (WARNING: Graphic/NSFW) of the May 10 incident while helping a woman who was being assaulted at the 16th Street Mission station. A BART maintenance worker can be seen trying to intervene as Garizabalo attacks other passengers. BART and San Francisco police arrived after about eight minutes.
Friends say Garizabalo, a circus performer, also goes by Yeiner Perez. They say the episode was strongly out of character.
The BART union representing station agents, Amalgamated Transit Union, says this kind of threat to agents and passengers is all too common.
"I've been an agent for 22 years; this is not something that's [gasp] an 'a-ha' moment for me, I live it, I breathe it, my co-workers do the same, as front line workers, and not just with agents, train operators are confronted with a variety of issues as well," ATU Local 1555 spokesperson Antonette Bryant said.
ATU is currently in contract negotiations with BART and is using the video to bolster its case for more safety measures.
Investigators for the District Attorney's office are urging anyone who witnessed the incident to call them at 415-553-1030.