The family of a Connecticut teenager who was shot and killed by police last Tuesday say they have been lied to by officers about how he died, after bystander footage filmed at the scene was made public over the weekend.

“We weren’t given the truth. We were lied to from the moment the incident happened,” said Giovanni Rivera, a relative of the victim, 15-year-old Jayson Negron.

Police in Bridgeport fired into the car Negron was driving after, they said, he backed his vehicle into an officer and refused calls to stop. Police say the car was stolen.

Rivera said police told him and other family members that Negron was struck in the head by an officer’s bullet and died instantly.

But Rivera said a video he uploaded to social media, taken by a bystander, raised questions about how Negron died. A figure, thought to be Negron, can be seen handcuffed, lying on the ground, as an officer stands over his body.

The shaky video pans away from Negron’s body for a moment, and when it returns a few seconds later, Negron’s head is facing in the other direction. Negron’s body was left on the pavement for upwards of six hours before being removed. Police attributed this to “evidence-gathering”.

“Nobody called an ambulance. Nobody treated his wounds. They let him bleed out on the concrete,” Rivera said.

Negron died from a gunshot wound to the chest, according to a postmortem.

Rivera said he received the video from a friend of the family who saw the incident but wanted to remain anonymous. “Bridgeport is a very small town, everybody knows everybody, and this happened on one of our busiest streets. A lot of people were there,” Rivera said.

Negron was the son of Rivera’s cousin, making Negron Rivera’s first cousin once removed. Rivera told the Guardian that the two were close and that he used to babysit Negron when he was younger. He has been the primary spokesperson for the family since the shooting.

The police department did not respond to a request for comment.

A spokesperson for Bridgeport’s mayor, Joseph Ganim, said the mayor found it “unacceptable” that it had taken police so long to move the body from the scene, but declined any further comment.

State police officials, who are handling the investigation, said the vehicle Negron was driving failed to stop when officers tried to pull it over and eventually traveled the wrong way down a busy street, striking several vehicles.

James Boulay has been identified by police as the officer who was struck by Negron’s vehicle, and the one who fired the fatal shots. A passenger in Negron’s car, 21-year-old Julian Fyffe, was also struck but did not sustain life-threatening injuries. Two Bridgeport police officers sustained minor injuries as well.