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18-year-old Nia Wilson was killed and her sister was hurt when they were stabbed on the platform at the MacArthur BART station
The stabbing is being described as a random and "vicious" attack
The suspect, 27-year-old John Lee Cowell, was arrested at the Pleasant Hill station without incident Monday evening.
Police on Monday evening arrested a 27-year-old man who they say is responsible for an unprovoked stabbing attack that left an 18-year-old woman dead and her sister wounded at the MacArthur BART station in Oakland.
BART police arrested John Lee Cowell without incident on an Antioch-bound BART train at the Pleasant Hill station about 6:30 p.m., the agency said. The arrest came as scores of people gathered together at the Oakland station to pay their respects to Nia Wilson, the young woman who died.
BART police Chief Carlos Rojas said his department received an anonymous tip from a rider who saw Cowell on a Richmond-bound train at the Coliseum station. When that train stopped at the MacArthur station, officers searched it but did not find Cowell.
Another rider, Bri Spearman, then told police that the suspect boarded an Antioch-bound train, which officers intercepted at the Pleasant Hill station, Rojas said. Cowell was then detained and taken to the BART police station at Lake Merritt in Oakland for questioning.
The deadly stabbing Sunday night was labeled by BART officials as a random attack. Nia Wilson and her sister were on the platform when they were stabbed, according to BART. Wilson was pronounced dead at the scene. Her sister was taken to the hospital.
"It was, in my close to 30 years of police experience, probably one of the most vicious attacks that I've seen," Rojas said.
It appears at though the Wilson sisters and the alleged attacker jumped on a train in Concord and later hopped off in Oakland, according to BART. Surveillance video on the train and at the station's platform showed Cowell had been riding the same car as the sisters, but they did not interact.
The suspect then approached the women at 9:36 p.m. and "attacked them very quickly," leaving Wilson with a neck wound, according to Rojas.
Letifah Wilson, 26, said that she, Nia Wilson and a third sister had been returning from a family outing when they were "blindsided by a maniac."
"He didn't know us, we didn't know him,'' Wilson said.
Two officers at the station rushed to the aid of the women, but Nia Wilson died as a result of her injuries, according to Rojas.
Ansar Mohammed, the father of the victims, spoke out after the attack, calling it "a parent's worst nightmare."
"I never imagined myself going through nothing like this," Mohammed said. "That's my baby girl laying up there. I want justice for my daughter."
A vigil for Wilson Monday evening at the MacArthur BART station later spread into a march through Oakland streets. A "#SayHerName Nia Wilson" vigil was also planned late Monday in Sacramento.
The suspect in the stabbing fled the scene through the BART station's parking lot and removed his clothing in the station's parking structure, Rojas said.
Authorities believe that they have recovered the knife that was used in the attack, according to Rojas. It was found in a nearby construction site.
NBC Bay Area learned Monday that Cowell is no stranger to law enforcement. The Contra Costa County District Attorney’s Office said he was just released from prison in May after serving time for second degree armed robbery; authorities said he used a box cutter and replica gun to rob an El Cerrito Lucky’s in 2016. He was on probation for battery and drug convictions at the time.
A motive for the MacArthur station attack remains unclear.
Sunday night's fatal stabbing is the third homicide in five days at a BART station.
Last Wednesday at the Pleasant Hill station, a 50-year-old man was assaulted, suffering a bloody lip and cut to the back of his knee, police said. The next day, the man wasn't feeing well and went to the hospital but was released. The man was found dead in bed Friday, and an autopsy determined he died from an infection from the cut on his knee. The suspect is still at large, police said.
Early Saturday morning at the Bay Fair station, 47-year-old Don Stevens was punched in the face and hit his head on the ground. He was later declared brain dead, police said.
An active investigation into Sunday's stabbing attack is ongoing.
The Associated Press contributed to this report.