LATEST: #RIPNIAWILSON, Suspect is Still on The Run.

Authorities in Northern California say the man wanted in the fatal stabbing of a teenager at a subway station is a violent felon on parole.

Bay Area Rapid Transit Police Chief Carlos Rojas said Monday surveillance video shows 27-year-old John Cowell "struck very rapidly," stabbing 18-year-old Nia Wilson to death and injuring her sister, Latifa Wilson.

Rojas says detectives found a knife at a construction site near the MacArthur train station they believe was used in the attack.

The chiefs says surveillance video shows Cowell attacked the sisters quickly, stabbing them after they exited a train.

He says it was an "unprovoked, vicious attack" and that officials have not determined a motive.

Rojas says surveillance video also shows Cowell fleeing through a parking lot, where he changed his clothes.

The chief says investigators are trying to determine what led to the attack. Rojas says they have no information it was racially motivated, but they are not discarding that factor as a possible motive. The Wilson sisters are black, and Cowell is white.

"Up to this point we don't have any information that was race-motivated, but we can't discard it.," he said.

 Police in Northern California have identified a man suspected of fatally stabbing a teenager at a Northern California train station as 27-year-old John Cowell.

Bay Area Rapid Transit police on Monday released three surveillance video images of Cowell, including one that shows him at MacArthur station Sunday night, when the teenager and her sister were stabbed on a platform after exiting the train.

The photograph shows Cowell wearing a gray and white track suit and carrying a backpack.

BART Police Chief Carlos Rojas described Cowell as "a violent felon who is currently on parole."

Police didn't identify the victims, but their relatives say they were 18-year-old Nia Wilson, who died, and her sister, 21-year-old Tashiya Wilson. Tashiya Wilson was hospitalized.

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