An Uber driver has been charged with manslaughter in the death of a 15-year-old passenger he allegedly let ride on the roof his vehicle on Long Island a month and a half ago, the Suffolk County district attorney's office said Monday. 

Ryan Mullen had been riding on the roof of the Danyal Cheema's vehicle Sept. 23 in Huntington Station; he fell off and hit his head on the road, then died of injuries stemming from the trauma, Suffolk County District Attorney Tim Sini said. 

Sini said Mullen and two friends -- both 16 -- had spent the night out partying in the Cold Spring Harbor area. After the last party, they called for an Uber. Cheema, 25, picked them up. They went to a 7-Eleven, then, according to Sini, asked the driver to "car surf." They offered Cheema $70 to let them do it. 

The transaction was not made then, Sini said. At some point later, the boys revisited the proposition, offering to pay Cheema $40 to let them ride on top of the car as he drove the vehicle. It wasn't clear if Cheema allegedly immediately accepted the money, but at some point, Mullen and another boy were on top of the car as Cheema drove. Mullen fell off and hit his head on the pavement. 

It was all caught on Snapchat, Sini said.

Mullen was taken home and died that night. The medical examiner's office ruled the boy's cause of death to be blunt force trauma to the head. Sini acknowledged that poor decisions were made all around, but said Cheema was an adult and the boys were minors. As an Uber driver, too, Cheema was entrusted to get his passengers to their destinations safely, Sini added.

"This is a case that obviously has tragic consequences for the Mullen family. A young boy is no longer with us because of the actions of the defendant," the district attorney said after Cheema's arraignment Monday.

Cheema, 25, pleaded not guilty to the charge, Newsday reported. Information on a possible attorney for him wasn't immediately available. 

It wasn't clear how long he had been with Uber. The ride-share company told News 4 it has been cooperating with law enforcement on the investigation.

"Words cannot describe how deeply troubled we are by this incident," an Uber spokesperson said. "Our thoughts are with the rider’s family during this difficult time. This driver has been permanently removed from the app."