Wasni climbed into the car. About two minutes later, as the car reached an intersection a few blocks away, she began stabbing and hacking at the driver from the back seat, prosecutors said at a news conference.
The bleeding driver, 34-year-old Grant Nelson, managed to pull the car into a nearby condominium building driveway. He ran to the lobby entrance, banged on the door and screamed.
"Help me," Nelson shouted, "Help me, I'm going to die."
Meanwhile, Wasni allegedly tried to flee by taking the wheel of the car, but soon rammed into a median and took off on foot. After residents called 911, police arrived to find a bloodstained car, and a trail of blood leading from the parkway around the side of the building.
There they found Nelson in the grass in a pool of his own blood, suffering from deep stab wounds and hacking wounds to his arms, side, head and chest. He was coherent enough to describe his assailant to police and what happened, but he would later die in a hospital.
Police found Wasni after identifying her from the Uber app on the driver's phone, which he left in the car. She was crouching behind a building near where she'd abandoned the car, holding a machete in one hand and knife in the other. She wore only a bra and leggings - a Chicago Cubs shirt was found nearby, the Chicago Tribune reported.
When she repeatedly refused to drop her weapons, police used a stun gun on her and took her into custody. They would later find surveillance video from Walmart capturing Wasni stealing the weapons while wearing a Cubs shirt.
Authorities charged Wasni as an adult with first-degree murder, the Chicago Tribune reported. A judge called the attack "extremely violent" and ordered her to be held without bail. She will be held in a juvenile facility, the Tribune reported. She appeared in court Wednesday in a white jail jumpsuit, her blond hair disheveled and her eyes kept mostly to the floor.
Prosecutors called the attack "heinous" and "not provoked in any manner."
Wasni lives with a single mother and is a student at Taft High School in Chicago, her public defender said in court, according to the Chicago Tribune. She was in violation of the company's 18-and-older age restriction for riders. Access to the service can be removed if a rider is found to be underage.
An Uber spokeswoman said in a statement to the Chicago Tribune the company is "heartbroken by the loss of one of our partners, Grant Nelson. Our deepest sympathies and prayers are with his family and loved ones during this incredibly difficult time."
The ride-hailing company - embattled from a number of recent internal struggles and controversies - has previously made headlines regarding allegations that its drivers assaulted passengers. And the shocking incident spurred the question: why would a teenage girl - seemingly unprovoked - brutally attack a complete stranger?
Grant Nelson's sister, Alex Nelson, said in a news conference Wednesday the details of the attack were "horrifying and saddening," and that "obviously this is a time of heartbreak and tremendous loss for us."
"Grant was an extraordinary figure in our lives," she said. "He was a gentle man. He was a good man."
Grant Nelson, who lived with his parents in Wilmette, just north of Chicago, had a wide range of interests - from animals to classical opera to military history.
"We don't have any answers," Alex Nelson said.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)