Mahesh Wickramasingha, 30, died after being stabbed in the throat by 19-year-old Sam Harrison on 29 November 2011.
Harrison denied murder but pleaded guilty to manslaughter at Liverpool Crown Court.
The jury accepted that Harrison had not meant to kill his victim. He was ordered to serve ten years in a youth offenders institution.
On sentencing, the judge described it as a “merciful verdict”.
During his trial, Harrison, who was described by the prosecution as a gambling addict, admitted carrying out the attack on the father-of-two as he worked at Stanley News in Huyton.
He told the court it was a robbery that went wrong, adding he only meant to frighten his victim and forgot he was carrying a knife.
Det Ch Insp Phil McEwan said: “This was a brutal, unprovoked and senseless attack on an innocent young family man.
“Mahesh was simply going about duties at the newsagents where he worked when Harrison walked in, armed with a knife, and stabbed him fatally in the neck.”
A year before the killing, Mr Wickramasingha pawned his possessions and borrowed money to get to the UK from Sri Lanka. He wanted to earn enough to educate his two children and build a home for his family.
Ch Supt Mike Cloherty said the community had been shocked by Mr Wickramasingha’s death, describing the reaction from people in Huyton as “heart-warming”.
The community raised £23,000 to send to the victim’s family in Sri Lanka.
Mr Cloherty said: “[It] showed Mahesh had been welcomed by the community, having come to the UK to earn money for his family back home.
“Several fundraisers were organised to help his family financially during what has been a terrible time for them.” (BBC)