Bishal Gurung, 23, was chased down the embankment following a brawl at a Nepali New Year´s Eve party.
A drunken mob of around 15 men forced him to the ground and kicked and punched him after he was wrongly accused of hitting 20-year-old Kemik Thakali with a bottle.
Thakali, of Legion Court, Morden, and Rocky Gurung, 21, of Haig Place, Morden, and a third man then picked him up and dropped him in the water.
His body was found two weeks later when it was spotted floating by a member of the public.
Thakali and trainee accountant Gurung were cleared of murder but convicted of manslaughter.
Missan Gurung, 25, of Felixstowe Road, Abbey Wood,was jailed for nine months for violent disorder relating to the initial brawl.
At the Old Bailey on Friday, Judge Timothy Pontius said all the defendants are of previous exemplary character.
“You acted in a way that was out of character, all of which can be said of Bishal Gurung, the victim of your drunken aggression,” he said.
“It was an entirely unjustifiable, unprovoked and senseless attack, and he paid with his life, therefore the case is all the more tragic, not only for him but for you three and your families.”
He said they had not intended to cause serious harm or that he should die.
The defendants all come from families of Gurkhas, with Missan Gurung´s father serving in the regiment for 28 years, and his brother a serving soldier who has just returned from Afghanistan.
Judge Pontius said: “´Their own shame at your appalling behavior was plain, as was their dignity and respect for the court.
I´ve lost everything: Victim´s mom
In a victim impact statement to the court, Bishal´s mother, Sardha Gurung who lives in Nepal, said.
“I am unable to express my pain on paper.
“When my husband died, my son was three, and my daughter was four.”
She said she devoted all her energies to bringing them up.
“Today all my dreams have been shattered,” she said. “They say everyone´s destiny is written by God, but in my case, me and my son´s destiny has been written by these men. For other people, a man has died, but for me, I´ve lost everything.”
How it began
The court heard that trouble flared at a Nepali New Year´s Eve party on board the Yacht Club, a floating bar by Waterloo Bridge, in the early hours of April 13 last year.
Prosecutor Jonathan Laidlaw QC told jurors: "As the partygoers left there was an altercation between Bishal and the second defendant, Kemik.”
A fight broke out and Kemik complained he had been hit with a bottle.
Although another partygoer later claimed he was responsible for the injury, Kemik blamed Bishal.
Laidlaw said about 15 young men chased him [Gurung] along the embankment, where he was knocked to the ground and beaten.
The following day Kemik went to hospital about his head wound, claiming to have fallen over while drunk.
An hour later, a member of the public reported the attack to police, but no crime scene was set up because the body was not found for two weeks.
When the murder investigation began it was impossible to gather forensic evidence as the route of the London Marathon ran directly along the stretch of river where it took place, and spectators had disturbed the scene.
Rocky Gurung told police after his arrest he did not see the fight because he was tending to the injury to Kemik Thakali.
Missan Gurung, Roman Thapa, 21, of Balgowan Street, Plumstead, southeast London; Sushant Gurung, 22, of Halesowen Rd, Morden; and Lav Gurung, 21, of Princes Road, Feltham, Middlesex, were cleared of murder due to lack of evidence. Arjun Gurung, who is also accused of manslaughter, fled to Nepal and has not been heard from since.
Related story
Corporate Manslaughter Legislation: A Cup of Tea?
