"It's rare that we have a homicide so, of course, this is ramped up to the highest priority when you have three deaths", he said.
When the sisters got off their train at the MacArthur station, they became the victims of what Oakland Mayor Libby Schaaf has denounced as a "senseless act of violence".
Police identified the suspect as John Cowell, 27, who was taken into custody Monday, according to BART police. Cowell was arrested without any trouble on an Antioch-bound train at the Pleasant Hill/Contra Costa Centre station.
Authorities say Cowell had served time for second-degree robbery and was released from prison on May 6. She told ABC7 that Cowell attacked her sister suddenly and when she looked back, he was wiping blood from a knife.
Cowell has a violent criminal history and was on parole.
Cowell is considered risky.
Sadly, Nia was killed in the attack.
Beilal Chatila, an Oakland-based lawyer, said he was disappointed how some media outlets portrayed Wilson, referring to an image showing her posing with a gun-shaped phone case instead of all the other pictures "they could have chosen from".
Letifah told ABC 7 her sister's nickname was PG, short for "pretty girl".
Nia and Letifah Wilson were on the Bay Area Rapid Transit in Oakland, California, on Sunday (July 22), on their way home from meeting with family.
Mass protests have spread across Oakland demanding justice for the murdered teen.
A cousin had previously identified 21-year-old Tashiya Wilson as the wounded sister, but authorities later said Lahtifa Wilson had been hurt.
Prosecutors will seek a life sentence against a parolee charged with murder and attempted murder in the unprovoked stabbing of two young women at a subway station, a Northern California district attorney said Wednesday.
Writer and civil rights activist Shaun King shared the story on Twitter Monday, urging people to help find Cowell.
BART Police Chief Carlos Rojas called it "one of the most vicious attacks I've ever seen".
As to what led to Sunday night's stabbing, police still don't have a motive.
Rojas said that security footage showed Cowell taking off his clothes after the stabbing, which the police chief said was a sign of the suspect's "consciousness of guilt".
According to CBS, Rojas was not able to confirm if the attack was based on racial hostility, but is considering all options in the investigation.
Officers on Monday were watching several addresses for him in two counties, but he is also listed as homeless, Rojas said. Cowell was white and the two victims were black.
The photograph shows Cowell wearing a gray and white track suit and carrying a backpack.
Items comprising the makeshift memorial were placed there there to commemorate 18-year-old Nia Wilson, fatally stabbed Sunday night at the station Sunday night by a stranger. Lahtifa Wilson was later released from the hospital. She said the Wilson sisters were returning home after celebrating Nia's late boyfriend's birthday.
Police said two people were detained when a small scuffle broke out. He said BART police arrived and began performing CPR on one of the victims. Both sisters were stabbed in the neck but only Nia died.
A cousin, Ebony Monroe, told the Chronicle that Wilson was a "beautiful, sweet person" who "didn't deserve this".
Wilson's death is the third linked to the Bay Area rail in less than a week. He is described as a white male in his twenties or thirties with a heavy-set build.