Two teenage killers were filmed bumping fists shortly after they had stabbed an 18-year-old man to death.
William Haines, 18, and a 17-year-old accomplice launched an unprovoked attack on victim Yusuf Mohamed in Shepherd's Bush, west London, on June 26, 2019.
Haines was convicted of murder and knife possession at the Old Bailey on Friday, while the 17-year-old, whose details have been omitted for legal reasons, was found not guilty of murder after already admitting manslaughter and possessing a knife.
Both of them will be sentenced on February 24.
In CCTV footage played in court, the suspects were seen bumping fists after running from the scene of the stabbing.
Mr Mohamed was attacked "for no obvious reason" while walking with friends on Uxbridge Road, the court heard.
Haines attacked him first after crossing the street, stabbing him in the heart with "brutal efficiency".
Prosecutor Bill Emlyn Jones told jurors: "Yusuf Mohamed had no time to run away, he had no time to do anything to protect himself. Unlike his attackers, he was not carrying a weapon.
“He stood no chance."
Mr Jones added: "Seeing Yusuf collapse to the floor, and as Yusuf desperately tried to retreat, crawling backwards on his elbows, (the 17-year-old) took out his own knife and followed him, stabbing him in the leg as he lay defenceless.
"As the two young men ran away, tucking their knives back out of sight, they gave each other a fist bump as if to say, 'Well done us'."
Mr Mohamed died from his injuries in the hospital later in the night.
Detective Chief Inspector Rob Pack, from Specialist Crime, who led the investigation, said: “This was a savage and callous attack where a young man was set upon in the street and lost his life in a matter of seconds.
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“To this day, the motive for the killing is unclear.
“Both defendants clearly felt they could carry and use knives with impunity.
“That they congratulated themselves with a fist bump and smiles having so brutally taken a life is beyond comprehension.
“Today’s conviction brings justice for Yusuf and his family and, again, highlights the Met’s determination to tackle the scourge of knife crime.”