Conversation so far:
What happened during the aftermath of Euronymous' murder?
Vikernes was arrested on 19 August 1993 in Bergen.
How did Vikernes, Blackthorn and a third person plan the murder of Euronymous?
Someone stayed at Vikernes's apartment as an alibi. He was to rent films, play them in the apartment, and withdraw money from Vikernes' credit card as an alibi.
Did the police question Blackthorn and Faust in connection with Euronymous' murder?
Many members of the scene, including Blackthorn and Faust, were also taken in for questioning.
What does the latter refer to when Vikernes confesses at Euronymous' murder trial?
The latter refers to Vikernes confessing to the theft and storage of 150 kg of explosives, but not to murder and arseny.

Question: Who was Blackthorn's friend?
Self-contained rewrite: Who was Blackthorn's friend that helped in Euronymous' murder?