During his evidence, former bouncer Brown told the court he had “no recollection” of stabbing Johnston but did remember removing the knife from him.
He said he attributed the stabbing to Crowley, the occultist, and claimed friends had told him of previous incidents in which he was “possessed” by him.
Brown also said he did Johnston a “favour” by removing his ring finger and consuming it.
He claimed Crowley was going to “take his [Johnston’s] soul”.
Brown was arrested after being found sleeping in his stepmother’s attic.
After the attack, he was found to have texted a friend about Johnston, saying “he sleeps forever”.
Brown had previously been jailed for offences involving young girls.
His defence advocate, Thomas Ross KC, said Brown been affected by mental health issues since he was a young, but had not helped himself by “lapses” in taking medication.
The judge excused the jurors from serving again for life due to the “harrowing and graphic” evidence they had heard.
Sentencing, Lord Mulholland told Brown: “This was a sustained, merciless and vicious attack on a defenceless man in his own home.
“It was motivated by a desire to punish the victim for what you believed had happened to your stepmother.”
