A college student killed by a stray bullet outside a West Philadelphia apartment building early Saturday was leaving a friend's birthday party when shots were fired from inside a car, police said Monday.

Police believe two passengers in the car were firing into the crowd where Zykia Sanders, 22, was standing with friends shortly after 2 a.m. on the 4400 block of Holden Street, Homicide Unit Capt. James Clark said at a news conference Monday.

Police do not know whom the shooters were targeting, "but what we do know is Zykia was not the intended target," Clark said. He announced a $20,000 reward for information leading to the arrest of Sanders' killer, saying police were still trying to track down witnesses to the "senseless murder."

"We need them to come forward and tell us what they know," Clark said.

The two shooters fired between 15 and 20 rounds out the windows of a four-door sedan being driven by a third person, Clark said. He said the shooters were likely aiming for someone in the crowd.

Sanders, who was shot in the back while fleeing, was the only person injured by the gunfire, Clark said. She was pronounced dead at the Hospital of the University of Pennsylvania.

For Sanders' mother, the pain of losing her daughter has been complicated by the frustration of not knowing who is responsible.

"I'm not going to feel right until they catch him," Tameka Jamaladdin said Monday. "I don't even feel right being outside."

Jamaladdin said her daughter, who police said had no run-ins with the law, had been working toward a bachelor's degree after studying psychology for three years at Indiana University of Pennsylvania, then transferring to the University of Phoenix.

"She was a beautiful person," Jamaladdin said.

Jamaladdin learned of the shooting at 2:30 a.m. Saturday, when her son got a phone call and woke her with the news, crying and running through the house.

Still half asleep, she said, she "just jumped up and started screaming, 'Who killed my daughter? Who killed my daughter?' "

Sanders' funeral will be at noon Tuesday at Masjid Ahlil Hadeeth, 67th Street and Woodland Avenue.

Anyone with information about the shooting is asked to call police at 215-686-3334.

Contact Maddie Hanna at 215-854-2771 or mhanna@phillynews.com