Video of a tracksuit-wearing thug punching a teenager to the ground and repeatedly kicking another victim has been released by police in a bid to trace the culprit.
Two 13-year-old boys were assaulted as they walked to catch a bus home following the finish of their after-school studies, Derbyshire Police said.
Officers have released CCTV footage of the 60 seconds of violence unleashed on the two youngsters near Derby's Council House as the first victim is sent reeling by a punch to the head and then shoved over nearby railings.
The attacker then chases his second victim, kicking the boy to the ground before appearing to land another swing at the youngster as he lies on the ground in the River Gardens.
As the boy gets to his feet to escape, the assailant swings another punch and the teenager goes to the floor a second time.
The incident happened at about 5.20pm on Tuesday December 8, not far from the city's Crown Court.
Police said they want to speak to a man, wearing a grey tracksuit, and two females in connection with the incident and have appealed for the public's help in identifying the trio.
The females, one of whom was riding a bicycle, are thought to be in their late teens.
Pc Steve Harper said: "The victims had stayed later at school completing extra work for their Duke of Edinburgh Award and were then walking through the River Gardens in order to get to the bus station and catch their bus home.
"The assault is particularly nasty as it appears completely unprovoked.
"We have released the CCTV, with the consent of the victims' parents, in the hope that anyone recognising the highlighted individuals or witnessing the incident will contact us."
Anyone with information is urged to call police on 101, quoting reference 53103/15, or contact Crimestoppers anonymously on 0800 555111.