Update, 1:10 p.m. Tuesday: John Lee Cowell has been booked under suspicion of first-degree murder and assault with a deadly weapon not a firearm following a fatal stabbing at Oakland's MacArthur BART Station on Sunday night.
Cowell is accused of stabbing Nia Wilson, 18, and her sister, Lahtifa Wilson, 26. Nia died at the scene. Lahtifa was critically injured and has been released from the hospital.
Alameda County sheriff's Sgt. Ray Kelly said Cowell is being held in protective custody at Santa Rita Jail "based on the severity of his charges and the amount of public attention this case is getting."
"There's people within the jail, I'm sure if they could take a shot at Mr. Cowell, they probably would based on a lot of the sentiment that's out there right now," Kelly said.
Cowell is expected to be arraigned on Wednesday morning. Kelly said the Sheriff's Department expects the arraignment will draw large crowds, and the department will likely have extra deputies at the courthouse for security.
Update, 8:30 p.m. Monday: BART says its police officers arrested murder suspect John Lee Cowell at the system's Pleasant Hill Station.
BART said officers took Cowell into custody "without incident" after an anonymous tip from a passenger. Cowell, who police say was captured on surveillance video Sunday night stabbing two women at Oakland's MacArthur Station, was aboard an Antioch-bound train when he was arrested.
Nia Wilson, 18, of Oakland, died in the Sunday night attack. Her sister, Lahtifa Wilson, 26, was critically injured.
BART Police Chief Carlos Rojas said during a media briefing in Oakland that two officers found Cowell during a search of the train, which had been held at Pleasant Hill following a passenger's call that the murder suspect was aboard.
Rojas said that Cowell readily admitted his identity and provided a California ID card when officers requested it. Rojas added that Cowell was unarmed when officers detained him around 6:30 p.m.
Meantime, a vigil for the stabbing victims at MacArthur Station early Monday evening was followed by a march to downtown Oakland. East Bay Express reporter Darwin BondGraham estimated the crowd that moved south on Telegraph Avenue at 1,000.
KQED's Alex Helmick said several dozen people later gathered at 20th and Broadway, shouting "Pigs go home," prompting a contingent of five BART police officers to leave the area.
Helicopter video from KTVU and ABC7 showed about 50 people gathered nearby, at 17th Street and Telegraph Avenue, with dozens more facing a police line farther down Broadway.
Original post, last updated 3:30 p.m. Monday: Police are searching for a 27-year-old man they say escaped after fatally stabbing an Oakland teenager and seriously wounding her sister at the transit agency's MacArthur Station.
BART Police Chief Carlos Rojas said in a media briefing Monday afternoon that the suspect, identified as John Lee Cowell, was seen in surveillance video attacking the two victims, then changing clothes as he fled through a nearby parking structure.
BART also disclosed Monday the deaths of two other patrons that occurred in unrelated incidents over the past week.
According to a BART statement on the Sunday night stabbing, the suspect boarded a train with the victims at the system's Concord Station.
BART said transit police officers who were already at MacArthur were alerted at 9:36 p.m. Sunday about a man with a knife on one the station's two platforms. When they responded, they found Nia Wilson, 18, of Oakland, and her 26-year-old sister, Lahtifa, suffering from stab wounds.
Rojas said the two women, along with a third sister, were on the platform to transfer to another train when the suspect approached them with a knife and "struck very rapidly." He called it "one of the most vicious attacks I've seen" in nearly 30 years of police experience.
"It was reminiscent of a prison yard assault, where you have an individual with a sharp object or a shank," Rojas said. "And they do their attack so quickly that before anybody can really react, the person takes off running."
Nia Wilson died at the scene. Her sister was rushed to a hospital with life-threatening injuries.
BART said officers identified Cowell from surveillance images captured by onboard and station platform cameras. They described Cowell as white, 5 feet 8 inches tall, weighing 190 pounds, with short, dark hair and a closely cropped beard and mustache.
Rojas said Cowell, who was described as a transient, is "a violent felon who is currently on parole." He said officers had found a knife they believe to be the weapon used in the attack from a construction site adjacent to MacArthur Station.
BART police said Cowell should be considered dangerous and anyone who sees him should immediately call 911.
Rojas said the motive for the attack was unknown.
Daryle Allums, Nia Wilson's godfather and a member of Oakland's "Stop Killing Our Kids" anti-violence group, appeared with Rojas at the media briefing. He said Nia Wilson and her sister "didn't ask to get cut or stabbed. Those are baby girls. Those are our children."
In the midst of social media threads that have pointed to a possible racial motive for a white suspect's attack on black women, Allums said, "We need the community, especially the African-American community, to stand down. ... I'm in fear right now. We don't know if this was racist, we don't know if it was random, we don't know what it was."
He said Stop Killing Our Kids would hold a vigil at MacArthur Station from 4 p.m. to 7 p.m. Monday.
In answer to a reporter's question, Rojas said police don't have any information connecting Cowell to hate groups.
"But that's something we haven't taken off the table, and we'll look into that," he said. "I know there's been a lot of conversation on social media regarding that, but I don't have one piece of evidence that this is race-related."
BART Discloses Fatalities in Two Other Incidents
BART police also reported Monday that they were working to identify a suspect seen in a fatal assault early Saturday at Bay Fair Station in San Leandro. They said that at 1:20 a.m. Saturday, officers responded to a report of a man injured on the station platform.
The transit agency said a review of surveillance images showed that a man struck Don Stevens, 47, on the side of the head with a closed fist after an argument. Stevens struck his head on the concrete floor of the platform.
"The best way I could describe it is cold-cocking him in the side of the head," Rojas said. "It's completely unexpected."
Police officers performed CPR until paramedics arrived, BART said, but Stevens was declared brain-dead at a local hospital. He was removed from life support and died Sunday afternoon.
BART police describe the suspect as a black male, 5 feet 8 inches tall with a medium build, shoulder-length dreadlocks in a ponytail, and a scruffy beard. The suspect was wearing a white T-shirt and a green jacket at the time of the incident.
In a third incident, BART reported that Gerald Busbee, 51, of Pittsburg, died last week two days after suffering what appeared to be minor injuries in an altercation at the Pleasant Hill Station with a fellow passenger identified as Abdul Bey, 20.
Rojas said that Busbee was injured in a fight last Wednesday apparently provoked by what he described as "mad-dogging" -- a staredown -- between the two passengers. Busbee suffered a cut lip and a cut on his knee that Rojas described as about one-eighth of an inch long.
Bey was arrested after a lengthy foot pursuit, Rojas said. He was charged at the time with one count of battery on a transit passenger and five counts of resisting arrest.
Busbee later went to a local hospital, complaining he wasn't feeling well, Rojas said. He was sent home after an examination, but was found dead in bed at his home on Friday.
The BART chief said an autopsy had determined that the cause of death appeared to be an infection arising from the cut on Busbee's knee. He said the investigation is ongoing and BART police are conferring with Contra Costa authorities about charges in the case.
The three fatal incidents in less than a week appear unprecedented in BART history. The last incident in which a BART passenger died as a result of an attack by a fellow rider occurred in January 2016.
That's when Carlos Misael Funez-Romero, 19, of Antioch was shot and killed aboard a San Francisco-bound train pulling into the West Oakland station.
Prior to that killing, the most recent homicide aboard BART was believed to have occurred in the late 1990s.
The Funez-Romero killing has not been solved. However, the incident brought to light the fact that virtually all of the "cameras" aboard BART's train fleet were actually decoys.
The agency has since installed working cameras on all its cars.