Lewis Daynes, 19, had lured 14-year-old Breck Bednar back to his home in Essex after months of online contact via video games.
He then bound the youngster in duct tape and murdered him.
"I grabbed the knife and stabbed him in the back of the neck, I believe somewhere near the brain stem"
Now, following a trial at Chelmsford Crown Court, it has been revealed that Daynes made a chillingly calm phone call to police after the attack.
"I need you to send police and a forensic team to my address," he can be heard saying in a 999 call, just hours after he had slit his friend's throat and emailed pictures of his dying victim to two people.
Daynes then goes on to claim that he and the schoolboy had got into an "altercation", adding: "Only one of us came out alive."
Asked by the operator if he was saying he had killed somebody, he replied simply: "Yes, I am."
"I grabbed the knife and stabbed him in the back of the neck, I believe somewhere near the brain stem.
"I don't remember exactly what happened, but the fight ended with me cutting his throat."
After outlining his story in a calm and matter-of-fact tone, Daynes cut short the conversation, politely telling the call operator: "Thank you for your help."
LISTEN TO THE CALL FOR YOURSELF BELOW:
When police arrived at the house, they found a bin bag containing duct tape and later established that Daynes had used it to tie his victim up.
They also learned that he had submerged his computer in water, in a bid to destroy the evidence.
Daynes has now been sentenced to life in prison, and will serve at least 25 years behind bars.
Following the sentencing Detective Inspector Anne Cameron of Essex Police described the teenager as 'a dangerous and manipulative criminal'.
She said: "He used his substantial computer expertise and his knowledge of the world of social media to control everyone he came into contact with in his virtual world.
"Tragically, his downward spiral of depravity went even further and ended in the brutal murder of Breck Bednar, an innocent 14-year-old boy who had placed his trust in a man he considered to be a friend.
"Sadly, Daynes abused that trust in the most horrific way possible."