Heroin addict Lee Anderson, 31, plunged a knife into Javaid Ali, 48, in the Sunshine Grocers in Green Road, Paisley, on June 15, last year.
The High Court in Glasgow heard that there were no forensics at the shop to connect Anderson with the killing, but he confessed his guilt to his mother and brother.
He told them: "I done the shopkeeper."
Anderson told his brother that he got into a scuffle with Mr Ali after trying to steal drink from the shop.
Anderson told his brother that he lashed out as 17-stone Mr Ali was getting the better of him.
The jury accepted this version of events and found Anderson not guilty of Mr Ali's murder, but convicted him of culpable homicide.
Throughout his trial Anderson, of Foxbar, Paisley, denied attacking Mr Ali. He blamed other men for the killing.
After the verdict, prosecutor John Scullion revealed Anderson has a previous conviction for assault to disfigurement for which he received a six-year jail sentence.
Passing sentence, judge Sean Murphy QC told Anderson: "It is clear from the evidence we heard Javaid Ali was a popular and respected local figure.
"His loss is grave not only to his own family but to the local community."
There was a high profile police investigation into the killing of Mr Ali and an appeal was made to find his killer on the BBC's Crimewatch show.