Cain had claimed during his trial he had bravely ran into the burning house to rescue Mr Cooper after spotting the fire while walking past the house, smoking cannabis with his cousin.
But Cain had savagely beaten Mr Cooper first, breaking 23 ribs and dislodging several teeth, before slashing his neck, a court heard.
A post-mortem examination found the Sheffield man had no soot in his lungs and was most likely dead before the fire took hold.
Sheffield Crown Court previously heard a drunk Cain had begun “ranting and raving” about Mr Cooper after his neighbour’s nephew, Duane Cook, had moved in with him.
Mr Cook, who had lived with Mr Cooper previously, had taken his dogs with him and the animals were “causing a smell” at Cain’s home.
Graham Reeds QC, prosecuting, said: “The victim was killed in his own home which is a serious aggravating feature.
“The extent of the injuries and the nature of the attack show that the defendant inflicted physical suffering before the victim’s death. This is clearly an intention to kill.
“An attempt to dispose of the body and dispose of the evidence of what the defendant had done is another serious aggravating factor.”
In a statement from Mr Cooper’s sister, on behalf of the family, said: “As we approached the start of trial to determine who was responsible for my brother’s death, it was with a mixture of anticipation and dread.
“While we have wished for the day to come so we can try to find answers to our many questions, we also understood that the truth would be painful and difficult to hear.