BART police say Dolph has admitted to the stabbing but did not give a motive.
RELATED: Good Samaritan hailed as hero after stabbing at BART station in Oakland
"I looked to my left between the agent's booth and the wall, saw a woman getting stabbed," said Harris.
Mike Bertilacchi took cellphone video just after the attack.
"Basically it was blood everywhere. The lady who was stabbed was screaming," said Bertilacchi.
"I grabbed him, took control of his wrists, got the knife away from him and took him to the ground," said Harris.
Harris described the knife as a large fixed blade survival knife, he says maybe 9 inches long. Harris says he didn't think anything, he just reacted, in the process sustaining cuts to his hands.
Harris says BART police arrived in less than two minutes.
BART police and witnesses like Bertalacchi are crediting Harris and others with preventing a homicide.
"Very thankful for those people and what they did," said Bertalacchi.
"First responders, people that do it every day and don't get acknowledged, those are the heroes," said Harris.
A BART spokesperson says the woman in her 60s has been released from the hospital. Her brother, in his 50s, remains hospitalized in critical but stable condition.
As for why he put his own life at risk, Harris says he was attacked and stabbed in his 30s in the hallway of the building he lived.
"The hallway was lined with people watching and no one did anything, wasn't a very good feeling," said Harris.
Bertalacchi says he'll be more vigilant when riding BART.
"I'll keep riding BART. You can't live in fear, you gotta keep going," said Bertalacchi.
Dolph is facing attempted murder charges.
The attack was caught on BART surveillance video. BART police are not releasing the footage because of the open investigation.
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