A teenager who killed an 82-year-old with a single punch at Derby bus station has been sentenced to two years in a Young Offenders' Institute.
Omar Moumeche, 18, was found guilty of manslaughter in July this year.
CCTV footage released by Derbyshire Police following Moumeche's sentencing on Friday captured the moment Mr Clarke was surrounded by a group of three teenagers on May 6, 2021.
He is first seen interacting with the group in the Derbion shopping centre, when it is thought he challenged them for misbehaving on an escalator.
The youths are then seen following Mr Clarke to Derby bus station, where he is punched and falls to the floor.
Police were called to the bus station in the Morledge around 4.30pm on May 6, 2021.
Mr Clarke suffered serious injuries and was taken to hospital, where he died nine days later.
Moumeche, of James Close in Derby, was just 16 at the time of the offence.
Detective Inspector Mark Shaw, who led the investigation, said: “The defendant claimed he acted in self-defence, and the jury on the balance and high threshold required refused to accept his version of events."
Mr Clarke was described by police as "a well-known and loved friend and family member".
"Dennis’ family were present throughout the hearings and have acted with absolute dignity both throughout the trial and including at the time the guilty verdict was returned and I thank them for that," said DI Shaw on Friday.
“The tragic events of that day have had a devastating effect on both the families of Mr Clarke and of the defendant himself.
"Mr Moumeches’ actions in that moment will have lasting affects both short term whilst he is serving his custodial sentence, and post-sentence as he tries to move forward.
“I hope that this case will demonstrate how important it is to stop and take a moment before resolving any matters and avoid resorting to the level of violence and the consequences seen here.
“I would like to express my thanks to the family of Mr Clarke for the dignity shown throughout the entire criminal process and hope they can look to move forward and now focus on their fond memories of Dennis.”
No further action is being taken against two other teenage boys who were arrested at the time in connection with the incident, police confirmed.