He told Detective David Checketts he suffered rage-induced memory lapses that would see him "lash out at the first thing contactable", and the condition was exacerbated by alcohol consumption, he said.
Bloody footprints from Fahey's body leading to the bathroom showed Blackler tried to wash himself after the attack but he was not totally successful.
He got a taxi from his house to his then partner's address in Corstorphine that night, and when police worked out which cab he had used, they combed the car for evidence.
Forensic staff found traces of blood 600,000 million times more likely to be from Fahey than anyone else in the country on the passenger seat panel.
Blackler spoke to his girlfriend on the phone before getting to her house and sat up with her all night, the court heard.
She gave evidence that nothing was said about the violent incident over the course of the eight hours they spent together.
But her teenage daughter gave the jury a different story.
She said she overheard Blackler telling her mother he thought he had killed his best friend.
"He knew what he'd done. He knew why he'd done it," Crown prosecutor Robin Bates said in his closing address.
Defence counsel Anne Stevens argued Fahey's facial wounds were just as likely to have come from him drunkenly staggering around his messy home and falling over as they were from an assault.
She said the blood in the bathroom could just as easily have come from him trying to clean himself up before he collapsed and died of a heart attack in the lounge.
If Blackler had been responsible for the attack, his level of intoxication meant he could not have formed the requisite intent for the charge to be proven, she said.
But the jury disagreed.
For a guilty verdict on a charge of manslaughter the Crown had to prove beyond reasonable doubt that the unlawful act inflicted on the victim was a "substantial and operative cause of death".
While pathologist Dr Martin Sage could not make a definitive finding on what killed Fahey, he noted the man suffered severe heart problems as well as lung disease.
Though he described the cuts and bruises to the victim's face and the small broken bone in his throat as "non-fatal", he said there was nothing to indicate he would have died without the assault.
The video of Blackler's police interview saw him cry and sob repeated apologies to his dead flatmate.
"He was like my dad that I never had," he said.
Bates said he accepted Blackler did not mean to kill Fahey and that he was sorry for what he did.
"Remorse is slightly different from not intending to do something at the time," he said.
Blackler was remanded in custody and will be sentenced next month.
