Mario Toliver Jr. remains at large after his sister, 17-year-old Justice Toliver, was shot just after noon on Thursday inside the apartment they shared with their grandmother on Franklin Street in the city's Chinatown neighborhood.
Oakland police describe the 14-year-old as armed and dangerous.
"We have not recovered the firearm that was used in this homicide so that is a concern not only for law enforcement but for our community as well," Oakland police spokesperson Johnna Watson said.
Mario is five feet, five inches tall, 140 pounds with dark hair, brown eyes.
The surveillance cameras inside the apartment building caught Mario walking down the hallway on the fifth floor with a gun. He then ran out an emergency exit that leads to Franklin Street.
A cousin, 22-year-old Oakland resident Marianna Gaston, says she was told the siblings had argued over how Justice was bleaching Mario's clothes.
When she first heard about the shooting, Gaston said she thought it was "a joke" and asked, "Why would he kill her over that?"
Standing outside the 12-story apartment building several hours after the shooting, Gaston said, "Nothing makes sense. It doesn't add up."
The victim worked at a McDonald's restaurant on Market Street in Oakland. Justice Toliver also had a 3-year-old daughter.
Thursday night, family members were trying to convince the 14-year-old to turn himself in.
"We love you; we're hurting just like you are hurting, please do the right thing," grandmother Wanda Brown said.
Oakland police say their investigation into the shooting is ongoing and anyone with information about it should call their homicide division at (510) 238-3821.
For details on an online fundraiser for Justice and her child, click here.
(ABC7 News reporter Lyanne Melendez and Bay City News contributed to this report)