John McGeechan, 34, was found guilty last month of the murder of Ahmjid Ismail of Kirkland Stores in Maybole, Ayrshire (C-Store, May 2).
Judge Lady Clark told McGeechan he would spend a minimum of 20 years in prison before being eligible for parole.
After the sentencing Ahmjid's brother Amir said: "There is no doubt in my mind that the individual responsible for this crime is an evil, cold and pathetic coward.
"The family has been overwhelmed at the sheer volume of cards, flowers, letters, visits, calls, texts and general positive support that have been shown to date," he added.
"All of these have been of great comfort."