Idsinga says the remains of alleged victim Majeed Kayhan have not been identified.
McArthur, wearing an orange prison jump suit, appeared by video in a Toronto courtroom Wednesday morning to be charged with first-degree murder in the case of Abdulbasir Faizi, an Afghan immigrant who went missing in 2010.
In early March, police announced they had recovered at the remains of at least seven people from planters at a home on Mallory Crescent where McArthur kept his landscaping equipment.
Idsinga said the investigation has expanded to include 15 homicide cold cases from 1975 to 1997. "It didn't make sense that police had this theory that he ran away", she said.
His auto was found abandoned not far from McArthur's home.
Investigators have identified six sets of remains so far - 49-year-old Andrew Kinsman, 50-year-old Soroush Mahmudi, 40-year-old Skandaraj Navaratnam and now 44-year-old Esen, 42-year-old Faizi and 42-year-old Lisowick.
The latest charge has been laid in the death of Abdulbasir Faizi, a 42-year-old married father of two who vanished on December 29 2010. Police have said the man was dead when the picture was taken, but won't say when or how they obtained the image.
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In a statement, the pro-independence leadership in the region called for a two-day shutdown in protest against the killings. "The searches operation was called off by the army in the evening as no militant body was recovered", they said.
Lisowick, a homeless prostitute who struggled with drugs hadn't even been reported missing when police announced he was one of victims. The photo was released with the hope that a member of the public may be able to identify him.
The 2016 interaction was the second time police spoke with McArthur in the years before he was charged with murder.
Police previously seized planters from houses McArthur worked at from around Toronto but found no remains in those planters.
In the wake of escalating questions about the investigations into the disappearances of the missing people from Toronto's Gay Village, the Toronto police board voted unanimously last month to commission an external investigation into how the force conducts missing-persons probes.
Faizi's disappearance was being investigated by Toronto police in connection with the disappearance of Skandaraj Navaratnam and Majeed Kayhan, 58, under an investigation dubbed Project Houston.
"We've quite frankly never seen anything like it", Idsinga said.
He has been in custody since his arrest in January. "I think it's easily set the record for a forensic examination of an apartment".