"He was unarmed. And all this for a phone? It just doesn't even make sense."
The dispatch audio reveals the frantic response after the shooting.
"It's going to be one man shot in the chest," an officer can be heard reporting in one dispatch transmission.
Minutes later, another transmission provided new details from the scene.
"We have one male shot, one confirmed chest so far," a dispatcher said, adding that one casing was found in front of the address.
The audio also captures officers relaying witness information about the shooting.
"The offender then turned around and shot the male once in the chest and ran," an officer said over police radio.
Police confirmed to Fox News the shooter was wearing a black-colored hoodie.
In a later transmission, police described the suspect as a thin-built Black male approximately 5-foot-8 to 5-foot-9 who was last seen running westbound on DeFord Street.
Anna Schmidt said she believes someone knows who is responsible for her brother's death.
"I need everyone to help find them because someone knows them," she said. "Someone has to know who did it. Just bring some peace to my family. I pray every day that they find them."
According to investigators, Schmidt was walking home after watching the NBA Finals with friends when the robbery unfolded around 1:30 a.m. Saturday.
"We are heartbroken over the tragic death of William Schmidt and we share our deepest condolences with his family and friends," Penn State said in a statement.
The city of Philadelphia is offering a $20,000 reward for information leading to an arrest and conviction.
Billy's father, Bill Schmidt, told Cotton he found his son's cellphone shortly after the shooting and turned it over to investigators.
"I found the phone on 19th," he said. "I called police after. I didn't realize I touched it."
Bill Schmidt said investigators are attempting to recover DNA and fingerprint evidence from the device.
"They're trying to get DNA, and they have a print on the phone, but they don't know if it's mine, Billy's, or the person who threw it," he said. "But they're trying to get DNA off the phone."
The elder Schmidt described his son as a sports-loving Phillies and Eagles fan who sold baseball cards and was looking forward to graduating from Penn State.
"He loved sports. He was selling baseball cards. He was a senior at Penn State," Bill Schmidt said. "All he used to do was watch the Phillies and Eagles."
"He was just a really nice kid. I'm surprised he even went to chase, because he's not an aggressive kid at all. He's a wonderful kid."
The loss remains almost impossible for the family to comprehend.
"I would just tell him how much I love him and miss him, and to come home," Anna Schmidt said. "He needs to be here."
Bill Schmidt said investigators are attempting to recover forensic evidence from the device.
The grieving father also called on city leaders to do more to combat violent crime.
"They gotta clean the city up," he said. "To stop the violence. This can't happen every day."
Police have not announced any arrests in the case and continue to ask anyone with information to come forward.
Anyone with information is urged to contact the Philadelphia Police Department.