They moved inch by inch, meticulously scouring the floors, walls and ceilings, examining the furniture, searching inside dresser drawers, careful not to miss what may be key evidence inside the apartment of an alleged serial killer.

Virtually every day for the past four months, Toronto police forensic investigators have been at work inside Bruce McArthur’s two-bedroom 19th-floor apartment at 95 Thorncliffe Park Dr., documenting its contents and searching for evidence such as hair, blood, fingerprints, fibres and more.

Finally this week — after seizing a trove of 1,800 exhibits and taking more than 18,000 photographs — investigators finished the exacting task, completing a central part of what has become the largest forensic examination in Toronto police history.

“It’s certainly the largest I’ve ever seen,” Det. Sgt. Hank Idsinga said in an interview Tuesday.

Search warrant in hand, police descended on the concrete highrise apartment on Jan. 19, one day after McArthur was arrested and charged with first-degree murder in the deaths of Selim Esen and Andrew Kinsman. In the months since, McArthur has been charged with murdering six more men: Majeed Kayhan, Dean Lisowick, Soroush Mahmudi, Skandaraj Navaratnam, Abdulbasir Faizi and Kirushnakumar Kanagaratnam.

As the investigation has grown in scale — police have begun searches involving cadaver dogs at 75 properties linked to McArthur — a team of 10 was assigned to McArthur’s apartment, with two officers stationed outside the door 24 hours a day, seven days a week.

In part because of the sudden spike in resource-intensive probes including the McArthur investigation, Toronto police Chief Mark Saunders wrote in a recent report to the board that a variance to the police budget is needed. Saunders cites “recent high-profile cases” as being among the factors that have led to an estimated $3.8-million shortfall.

In the past six months, the Toronto police homicide squad has taken on three large-scale homicide investigations: McArthur, the ongoing probe into the deaths of billionaire couple Barry and Honey Sherman, and last month’s van rampage, in which driver Alek Minassian is charged with a slew of murder and attempted murder charges.

The police board meets Thursday to discuss Saunders’s budget report.

Toronto police have not released definitive information about where McArthur’s alleged killings took place. But forensic investigators went in assuming the possibility at least one murder had occurred inside as early as 2010 — when McArthur is alleged to have killed Navaratnam, the first of the eight men.

The thinking was that “if there’s one of Skanda Navaratnam’s hairs in that apartment, you better find it, no matter where it is,” Idsinga said.

Unlike other homicide scenes, where investigators would likely zero in on an area in an apartment where a forensic examination is necessary, the probe in McArthur’s apartment encompassed the entire unit. That required investigators to work their way from the front entrance inward — otherwise, they risked contaminating the space, Idsinga said.

For the same reason, it was usually only the two lead investigators working inside the apartment, though they could call upon other officers when necessary. “You want to minimize the number of people you have in that apartment,” Idsinga said.

Some of the evidence retrieved from the apartment will now be further tested, either at the Toronto police’s own forensic lab or at the Centre of Forensic Sciences.

McArthur’s unit has now been turned over to the property management company for the building. An employee of Leaside Towers, which includes 95 Thorncliffe Park Dr., said she had no comment when asked Tuesday if the unit will made available to rent.

Since McArthur’s arrest, the remains of seven men have been located inside large planters found on a Leaside property linked to McArthur, forensically identified through fingerprint, dental records or DNA testing. All but Kayhan’s remains have been identified.

Sources have previously told the Star that among the evidence collected by investigators were reams of digital images; photos of dead men were found on McArthur’s computer, according to a police source.

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Last week, police began using cadaver dogs to search other properties that may be linked to McArthur, either through his client list or tips from the public. Idsinga said that initial search with the dogs is expected to wrap up next week. After that, investigators may go back to locations where the dogs gave indications that more searching may be required.

In addition to the searches, police are investigating 25 cold cases dating to between 1975 and 1997 where there may be a possible connection to McArthur.