Wilson and her sister, 26-year-old Lahtifa Wilson, boarded the train at Concord Station at the same time as the suspect, who also got off the train at MacArthur Station at the same time, according to BART police.
Authorities say a man fatally stabbed an 18-year-old woman in the neck and wounded her sister as they waited for a train in Oakland.
Letifah Wilson told KGO-TV that the suspect "was wiping off his knife and stood at the stairs and just looked" after the attack.
Lahtifa Wilson, who is recovering from a stab wound to the neck, has since been released from a hospital.
Nia Wilson died at the scene and her sister has been hospitalized in critical condition, according to the publication.
Wilson said she told her sister she loved her.
Surveillance video on the train and at the station's platform showed Cowell had been riding the same auto as the sisters Sunday, but they did not interact, Rojas said.
As soon as they exited, Cowell reportedly attacked the women on the platform.
Police said an officer verified Cowell's probation status and then found drugs in his possession when he searched him.
Video surveillance indicates that Cowell allegedly entered the parking structure at the station and discarded his clothes.
Authorities said the suspect was released from prison only a few months prior after serving time for robbery, and they believe the attack to be random, according to ABC7 News.
The women's father, Ansar Mohammed, said one of his daughters called him, crying hysterically, and told him to get to the MacArthur station. "I hate to say that, but, you know, why would you choose two black girls?"
After attacking Nia and Letifah, he was arrested on charges of first-degree murder, assault with a deadly weapon and violation of parole.
Authorities arrested 27-year-old John Cowell on an Antioch-bound train on Monday night at a Bay Area Rapid Transit station about a dozen miles from Oakland. Alameda County court records also show several misdemeanors on his record related to vandalism, petty theft and possession of a controlled substance.
Investigators late Monday were still seeking a motive in the horrific attack.
"Cowell is white, 5' 8" tall, and weighs 190 pounds. He has short, dark hair, a closely cropped beard and a mustache.
"It's rare that we have a homicide, so of course this is ramped up to the highest priority when you have three deaths", Rojas said.
Cowell is considered risky. The attack, however, sparked a demonstration during a vigil at the transit station where Wilson, who was black, was killed.
Allums said, "We're asking the community to respect the family and don't put any blood on our hands". "Let's get this information to find out what really happened".
Rojas described the stabbings of the sisters as a "prison-style attack". Condolences go out to her friends and family, especially her sister, Malika for a speedy and full recovery. He drowned two years ago in a lake.
"All of a sudden, we transfer just to get blindsided by a maniac, for what I don't know", she said. BART police arrested the alleged suspect, John Cowell, on Monday evening. She recognized him as the man BART police were looking for and said she immediately had a reaction to seeing him.
"Everything that we've uncovered up to this point, we see no altercation", Rojas said at a press conference Monday.