A woman who witnessed the killing of a man who intervened during a theft on a San Francisco Bay Area commuter train is describing a horrific scene.

College student Sophia Humphrey says a barefoot Jermain Brim was moving in erratic, twitchy motions before he allegedly attacked Oliver Williams, 49, she told the San Francisco Chronicle in a story published Friday.

Williams stopped Brim, 39, from stealing the shoes of a sleeping homeless man and the two started fighting, authorities said. Brim wrestled a knife away from Williams and used it to fatally stab him Tuesday, according to Bay Area Transit Police.

Humphrey, a nursing student who uses a wheelchair, said several passengers begged Brim to stop but he did not listen and stabbed Williams in the neck at least five times.

She said other passengers fled the train when it pulled into the station, but Humphrey and another passenger stayed.

Humphrey, who is legally deaf but can read lips, said she texted police to stop the train and send an ambulance. After the train pulled into the station, Humphrey saw Brim flee, strip off his blue hoodie and run down the stairs.

Brim was wearing only pants when he was arrested near the station after authorities said he tried to steal a van at a car dealership.

He was charged Thursday with murder, two counts of attempted second-degree robbery and two counts of attempted carjacking. He did not enter a plea and refused to show his face in the courtroom, the Mercury News of San Jose reported. It was not immediately known if his attorney commented.

Humphrey said she lunged onto the floor and wriggled over to Williams and replaced his hands with her own to apply pressure to the wounds.

Two women came in from another train car and Humphrey asked them to call emergency services for an update on paramedics because it had been “several minutes” since she first called for help.

“I seriously wonder if there had been police officers nearby, or available first aid, there could have been some way to reduce the bleeding faster. Would they have been able to save him?” Humphrey asked.

Williams’s killing follows the death of 18-year-old Nia Wilson, who was stabbed last year in an unprovoked attack on her and her sister in an Oakland BART station.

John Cowell, a 28-year-old parolee arrested in Wilson’s killing, pleaded not guilty by reason of insanity Friday.