Animal rights groups, with the help of online sleuths, soon identified Magnotta, and Toronto police began investigating, news.com.au reported.
What they discovered was that Magnotta had dozens of aliases on more than 70 Facebook pages. He was a ghost, but he would soon emerge from the darkness with a more sinister video.
On May 25, 2012, an 11-minute video appeared online titled "1 Lunatic 1 Ice Pick". The video depicted the savage murder and dismembering of Chinese exchange student Lin Jun, 33.
Magnotta wasn't finished there. After cutting up Lin's body, he mailed parts of it to different organisations around Canada and then fled the country.
He would be captured at an internet cafe in Berlin where it was reported he was reading articles about himself.
The videos, the manhunt and Magnotta's bizarre behaviour are part of a new documentary that hits Netflix later this month.
Titled Don't F**k With Cats: Hunting an Internet Killer, it explores how "a twisted criminal's gruesome videos drive a group of amateur sleuths to launch a risky manhunt that pulls them into a dark underworld".
Director Mark Lewis told Deadline the documentary was "mind-blowing".
"It plays out like a real thriller, with twists and turns that no one will see coming, a cast of internet heroes whose resourcefulness will have you cheering from the sidelines, and a murderer whose true identity will have you gasping when he is finally unmasked."
Magnotta's crimes were revisited in graphic detail at his 2014 trial where he admitted to killing and cutting up the body of the computer engineering student but tried to lie to jurors about hearing voices in his head.
Magnotta spoke for the first time since he was jailed for life in a new book titled My Son, the Killer that features his mother.
He admits to lying to the jury.
"I have no mental illness whatsoever. I had to go with it, even though I didn't want to, but my lawyers pressured me into it," author Brian Whitney wrote.
"I told the doctors I had no mental illness. Even now in prison I take no medications, but the lawyers said our only chance was to go with the defence.
"I wish I didn't do it, I wish I testified and told the story my way."
"He'd [Lin] been decapitated and the pathologist wasn't sure if this had happened before or after he was dead," the newspaper reported.
"A month had passed before his severed head was discovered in a Montreal park."
The National Post last year wrote that Magnotta showed no sign of contrition. Whitney told the publication that he even thought he was a victim.
"He thinks society is sick – not him," Whitney said.
"He feels (or at least says) that people are obsessed with him, constantly making things up, gossiping about him, etc. I think there were definitely moments when I felt he was being deceitful, other times it seems like he actually believes what he is saying."
Magnotta's mother says her son is not a monster, but she grieves for his victim.
"I began to cry uncontrollably," she says in Whitney's book of the moment Magnotta was arrested.
"I cried for my son; I cried for Jun Lin and his family; I cried for my family, and I cried for myself."
Don't F**k With Cats lands on Netflix on December 18.