The 23-year-old Swede is charged with murdering his 32-year-old lover by cutting his throat with a knife, at his apartment on the Lidingö island in Stockholm on June 27th this year.
According to the man, who reported himself to police shortly after the incident, he then drank the victim's blood and painted the gory pentagram in his living room.
"When I saw the blood I had a vision that I had to drink it," said the accused in court as the trial into one of Sweden's most gruesome deaths began this week.
The court heard that the man, who suffers from a serious psychiatric disorder and admits to manslaughter but not murder, told police, in a total of 14-hour interrogation sessions, that he killed his victim – named in the Swedish media simply as 'Olle' – after hearing threatening voices in his head telling him to do so.
"I the light of his psychological ill health this is a deed that can only be classified as manslaughter," his lawyer Jonas Granfelt was quoted as saying by Swedish tabloid Aftonbladet on Tuesday.
However, according to prosecutor Pär Andersson, the killing had been planned in advance, with Google searches for 'cut throat' and 'sentry killing' found on the man's computer.
While Sweden is known for being one of the most tolerant and gender equal nations in the world, the prosecutor told Aftonbladet he believed the man had killed his victim to cover up their gay relationship. He added that he would appeal the psychiatric report.
"I believe that it is a fairly common argument in cases like this that you hear voices of various kinds. A more likely motive may have been to hid this sexual relationship they had. A relationship which he, in several police interrogations, denied they had had before he confirmed it and said he was ashamed of it," said Andersson.
The trial continues.