Detective Sergeant Hank Idsinga said police knew "something was up" while investigating the alleged serial killer Bruce McArthur.
McArthur is currently being accused of murdering eight men after their remains were found in a number of properties owned by the landscaper across Toronto, and Idsinga "always had a feeling" that someone was targeting the Gay Village.
He told CBC News: "We've always had that feeling. Until I have evidence, I can't say it. And that's what we dig for.
"We investigated that piece of evidence for six months until we were able to eliminate it.
"It's easy to say in hindsight now, 'Well, you should have known something is up'.
"Well, we did know that something was up, we just didn't know what it was and we didn't have any evidence of what was going on."
Police have been searching properties McArthur had worked at for remains after having found at least six other sets of remains, three of which were identified as belonging to Soroush Marmudi, Andrew Kinsman and Skandaraj Navaratnam.
McArthur was arrested and charged with the murders of two men in January, before being charged with the murders of four more men whose remains were found in the garden planters.
And Idsinga said it was "sickening" when he opened a planter in the morgue and found a human skull.
He said: "It was sickening, and it was angering. I was very angry at the time. That this had happened.
"That this had gone on in this city... I've been working in the city for almost 30 years doing police work, trying to keep the city safe.
"And realising this has gone on, it angers me."
Recently, the alleged serial killer was charged for the death of Kirushna Kumar Kanagaratnam, but Idsinga said they are "still looking" into his background.
He said: "We're still looking into Mr Kanagaratnam's background and his movements here in Canada.
"I don't know the status of his immigration claim. We are aware that he came here in 2010 and we're trying to figure out what his movements were between 2010 and 2015.
"Hopefully we get some answers to those questions."
The prolific murders are being investigated by 10 full-time officers and it has turned its focus to cold cases as far back as 1975.
Between 1975 and 1978, 14 men from the Gay Village were found dead and at the time it was speculated that they died at the hands of a serial killer, though police never confirmed it.