A US animal rights group said they saw warning signs about Luka Magnotta when kitten killing videos began surfacing online in 2010.

The videos depict a man in a hoodie drowning the animals, suffocating them using a vacuum bag and also feeding kittens to a python.

Animal activists have connected the videos to Magnotta, but it has not been proven in court.

"It was like watching the worst horror movie ever," said Shane Barbi, who along with her twin sister Sia, were among the first people to find out who was behind the killings and alert the police.

"People who hate cats have control issues. My mom, who is a psychotherapist, said any addiction starts with control. It was creepy, it was like Silence of the Lambs."

The Barbi twins brought the footage to the FBI and was told it was not staged, but in order to prosecute the filmmaker, they would have to be brought to the U.S. But it never happened.

"They lured Luka into a chatroom because of a porn job offer," Barbi said.

He bragged about killing people, he said.

News about the grisly videos spread to other anti-animal abuse organizations, including Rescue Ink, who put up a $5,000 reward for the kitty killer's capture.

"When we were going back and forth with authorities, the only problem we had was they were not going to indict Luka to the US because of he was (allegedly) abusing animals," recalled Joe Panz, the founder of the animal rescue group.

"It wasn't a strong enough crime."

Rescue Ink - which is made of police, military officers, lawyers and private investigators - hired its own criminal profiler to assess Magnotta "with the many names he had."

"He was someone who was full of himself and would keep on going because he fed off power and all the attention," Panz said.

"It would keep growing because it wasn't enough."

Barbi said kitten killers need to be listed on a national violent offenders registry.

"If there's something that can be learned from this, (police) should be able to profile these people and permanently put them in the database," she said.

"Make them register, just like child molesters."