When police in Memphis launched the first SkyCop surveillance cameras in 2007, department chiefs could hardly have imagined the most horrific crime caught by the network after 16 years in operation would be carried out by its own officers.

The clearest video of the brutal January 7 attack that killed Tyre Nichols was filmed by one of the 2,100 cameras installed around the city at a cost of more than $10 million. 

They are supposed to make people safer. However, critics feel Americans are trading their privacy for a tool that helps catch criminals but struggles to fulfill its promise of preventing crime. 

Harrowing, high-definition footage captured by a SkyCop shows five Memphis PD officers take it in turns to punch, kick and pepper-spray Nichols in a brutal attack which lasted around five minutes.

The remainder of the 31-minute video shows Nichols, 29, dragged over to a nearby car and propped against it. Officers are recorded strolling around his slumped body as he writhes in agony. At one point, an officer lights a cigarette. Others repeatedly shine their flashlights into the young man's battered face while they wait for paramedics to arrive.