The Toronto police officer at the helm of the investigation into alleged serial killer Bruce McArthur said on Tuesday in a one-on-one interview with CBC's The National that if one of the victims had been reported missing even a week later than he was, McArthur might still be free.

"Andrew Kinsman was reported within 72 hours," said Det.-Sgt. Hank Idsinga, referring to one of five men McArthur is charged with killing. "A crucial piece of evidence was uncovered because of that immediate reporting.

"If he had been reported seven or eight days after he disappeared we wouldn't be here today," Idsinga said.

But while few days made all the difference in arresting McArthur, Idsinga said the investigation of the 66-year-old landscaper could take years.

"You stop when the evidence stops," he said. "You can't leave these families out there wondering."

McArthur faces first-degree murder charges in the cases of five men: Andrew Kinsman, 49, Selim Esen, 44, Majeed Kayhan, 58, Soroush Mahmudi, 50, and Dean Lisowick, 47.

Apartment search still ongoing

Police have already begun the time-consuming process of combing through outstanding missing persons cases, Idsinga said, revealing that investigators are looking at cases from as far back as the 1970s, when McArthur was in his twenties.

Investigators have also poured hundreds of hours into searching every "square inch" of McArthur's Toronto apartment and the properties of his landscaping clients.

Det.-Sgt. Hank Idsinga explains the time consuming process of examining the accused serial killer's apartment 0:52

The longtime homicide officer also shed some light on the timeline leading up to McArthur's Jan. 18 arrest, beginning with his connections to Project Houston, an investigation into three missing men with connections to the Gay Village that ran from 2012 to 2014.

CBC News had reported in late January that McArthur was in a romantic relationship with Skandaraj Navaratnam, who went missing in 2010 and whose case was part of the Project Houston investigation.

Idsinga said police were aware of their relationship, but wouldn't say whether police spoke with McArthur as part of Project Houston. He did say McArthur was never a suspect.

So did police consider at the time that a possible serial killer could be targeting men in the Village?

"To be accused of not considering that is in effect not accurate," he said. "We're human beings, of course are we thinking, is that a possibility?"

Ultimately, no evidence that the three men met with foul play was found at the time.

"I wish we had that evidence in 2013. I wish we could have stopped it in 2013," said Idsinga.

The day that 'changed everything'

McArthur came on the Toronto police's radar in earnest in September 2017, after evidence was discovered potentially linking him to the disappearance of Kinsman, Idsinga said.

In the early winter months, he became a suspect in Kinsman's disappearance, said Idsinga, and by mid-January, he was under full-time police surveillance.

Then came Jan. 17, the day which Idsinga said "changed everything."

Evidence linking Bruce McArthur to the deaths of Selim Esen and Andrew Kinsman was discovered in the course of a single day, Idsinga said. (Facebook/Canadian Press)

Two bombshells were discovered: first, evidence linking McArthur to the slaying of Selim Esen (who went missing on April 14, 2017), and then, later in the day, to Kinsman.

"January 17th was definitely a day that really changed the direction and the scope of the investigation," said Idsinga, who wouldn't elaborate on what that evidence was.

Why Idsinga is 'angry'

Since then, McArthur has been charged with three additional counts of first-degree murder, and the remains of at least six people have been found hidden in planters in a Leaside property where he worked as a landscaper. Only one set of those remains has been identified.

McArthur's alleged victims, from left to right: Selim Esen, Soroush Mahmudi, Dean Lisowick, Andrew Kinsman and Majeed Kayhan. (Toronto Police Service/AP)

Idsinga described learning that remains were hidden in the planters as a rare moment of on-the-job anger.

"I was angry that this had gone on in this city for some time," he said. "It's one thing to kill them. It's quite another to dismember them. And then it's quite another to really quite callously put those remains into planters on properties of different people around the city. I've never seen anything quite like that."