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OAKLAND, Calif. — A manhunt Monday ended in the arrest of a man suspected of fatally stabbing an 18-year-old woman and wounding her sister in an unprovoked attack at a BART station in Oakland — the third death in the transit system in a week.

John Lee Cowell, 27, boarded the same train as slain victim Nia Wilson and her two sisters at the Concord Station Sunday night, Bay Area Rapid Transit Police Chief Carlos Rojas said in a Monday news conference.

When all four of them got off six stops later at the MacArthur Station, where the sisters planned to transfer, Cowell is accused of “very rapidly” launching an attack on Nia and her 26-year-old sister Lahtifa Wilson. Still on the platform, he stabbed both several times with a knife, including in the neck, Rojas said.

“In my close to 30 years of police experience, it was one of the most vicious attacks that I’ve seen,” the chief said Monday.

Nia’s sister Nishiya came to her aid immediately, applying pressure to her neck wound, but the 18-year-old died at the scene. Lahtifa was taken to a nearby hospital, where she was in stable condition on Monday.

There was no form of dispute leading up to the incident, according to Rojas, who called it an “unprovoked, unwarranted, vicious attack.”

Other relatives told KPIX in San Francisco the teen had paused to help a woman struggling to exit the train with a stroller just before she was killed.

Nia’s godfather, Daryle Allums, called for the community to remain peaceful in the aftermath of the senseless attack, which he suggested may have been racially motivated.

“They didn’t ask to be stabbed, those are baby girls,” he said in the news conference. “We don’t know if it’s racist; we don’t know if it’s random.”

Detectives haven’t recovered evidence to indicate race was a motivating factor, but it’s not something investigators are “taking off the table,” Rojas said.

Rojas described Cowell as a “violent felon” who is currently on parole.

Following his swift attack, the suspect took off running before anyone in the station could react and fled through the BART parking lot, the chief said.

Surveillance video shows him leaving station and entering parking structure, where he stripped his clothing, which Rojas said he considers “consciousness of guilt.” Investigators also recovered knife that they believe was used in the crime at an adjacent construction site.

He was taken into custody on a murder warrant the following day, Monday, around 6:50 p.m. at the Pleasant Hill Station just north of Walnut Creek. Police did not immediately release further details on his arrest but thanked the transit services’ riders for remaining vigilant.

Cowell has several addresses throughout Contra Costa and Alameda counties but is listed as transient, Rojas said.

Nia had expressed concerns about the safety of the transit system before, her mother told KPIX.

“She was less than 100 pounds soaking wet. This man just came up and did all this to my baby,” Alicia Greyson told the station as tears streamed out her eyes. “My baby didn’t deserve this. She hated BART. She was always saying, ‘Mama, I’m scared of BART.’”

The teenager’s death was in fact the third to occur at a BART station last week.

The day before, on Saturday, July 21, a 47-year-old man was declared brain dead at a nearby hospital after being struck in the head and knocked to the ground on the Bay Fair Station platform in San Leandro. Officials have released a suspect description but no identified a suspect in that case.

And on Wednesday, July 18, a 51-year-old man was left with a bloody lip and cut on his knee after being assaulted at the Pleasant Hill Station. He was treated at a hospital the next day, but died at home in his bed Friday night because of an infection in the cut on his knee. A suspect is in custody in that case.