The primary investigator that helped put serial killer Bruce McArthur behind bars is leaving the homicide unit to work with Toronto Police Service’s canine unit, saying it was time for a change and some “therapeutic relief.”

Last week, McArthur was sentenced to life in prison with no chance of parole for 25 years. The sentencing came after the 67-year-old pleaded guilty to murdering Andrew Kinsman, Selim Esen, Majeed Kayhan, Soroush Mahmudi, Dean Lisowick, Skandaraj Navaratnam, Abdulbasir Faizi and Kirushna Kumar Kanagaratnam.

The eight men were killed between 2010 and 2017.

For the last year and a half, the investigation into McArthur and his eight victims has consumed much of Det. David Dickinson’s life. He was one of three officers who arrested McArthur as he was meeting up with a man identified by police as “John” on Jan. 18.

Dickinson said that one of the toughest moments in the investigation was after the serial killer’s arrest.

“There was a lot of criticism about our investigation or the fact that people believed that we potentially jeopardized their safety by, as they said, leaving him out there. It was tough to hear that because for months, all we did was try our hardest to protect the public.”

Dickinson would not discuss the conversations he had with McArthur during police interviews, but did say that he was “polite” and “inquisitive.”

“You know, interested in the investigation, interested in how we got the evidence we did,” he said.

The head of the homicide unit and the major case manager in the McArthur investigation Insp. Hank Idsinga said that these kind of cases have a lasting effect on officers.

“You’re looking at material that nobody wants to look at, but it comes with the job. And it's part of getting the job done and that's what we have to do,” he said.

Dickinson said that he had a strong support system throughout the McArthur investigation, but after five years with the homicide unit he has decided to move on. He was inspired to start working with cadaver dogs after watching the impact two dogs had on the McArthur investigation. The dogs helped locate human remains of McArthur’s victims on a Leaside property where he stored tools for his landscaping business.

“Working with them for as long as we did, my interest was sparked in the canine unit,” he said.

“I've been at homicide for five years, and it's had its stressful moments, and I think it was just time to change it up a little bit and might be a little therapeutic relief as well,” he said.

Dickinson said he is looking forward to completing his training and working with the dogs.

“Dogs love you all the time and are happy to see you and it just naturally brings a smile to your face,” he said.

“I'm just cresting that halfway mark in my career and I think there's still a lot of time to think about promotion and advancement, but right now I think it's important to do something for my family and myself for a bit.”

Dickinson starts full-time with the canine unit next Monday.

With files from CTV News Toronto's Tracy Tong