Luka Magnotta had sparked worries among Toronto police

Toronto police saw alleged killer Luka Rocco Magnotta as a growing danger to society months before the grisly slaying of Chinese student Jun Lin in late May, according to correspondence obtained by CBC's the fifth estate.

Magnotta has been charged with first-degree murder in the killing and dismemberment of the Concordia University student in a case that drew international attention. The Toronto-born man pleaded not guilty. His preliminary hearing is slated to begin in March 2013.

Correspondence between the Toronto police and an online group investigating Magnotta, and later obtained by CBC's the fifth estate, shows that a detective expressed concerns about Magnotta nearly three months before Lin's death in Montreal.

"I want to find this guy more than anyone out there," a Toronto police detective told the online activists in one email dated March 9, 2012. "Trust me, I want to bring him before the courts even if just to get him psychiatric help."

Magnotta was never found or questioned by police, until he was arrested in a Berlin cafe on June 4 following a massive global manhunt.

The fifth estate also obtained exclusive interviews with members of the anonymous online group who were tracking Magnotta in late 2010 and notified authorities in early 2011 — more than a year before Lin's death — about their concerns regarding Magnotta.