Open this photo in gallery Police investigate a home that accused serial killer Bruce McArthur worked at in Toronto on July 6, 2018. Carlo Allegri/Reuters

A Toronto police officer will be charged on Tuesday morning with insubordination and neglect of duty in connection with the investigation into serial killer Bruce McArthur.

News of the disciplinary procedure against Sergeant Paul Gauthier comes just three days after Mr. McArthur pleaded guilty to eight charges of first-degree murder, admitting he targeted Toronto’s gay village for nearly a decade.

Sgt. Gauthier’s lawyer, Lawrence Gridin, said the charge is connected to an incident in 2016. The Globe has previously reported that in 2016, Mr. McArthur was interviewed by police after a man said Mr. McArthur choked him during sex. No criminal charges were laid at the time.

Story continues below advertisement

“The decision not to charge Bruce McArthur for the 2016 incident was made in conjunction with Detective Gauthier’s supervisor and based on the information available at the time," Mr. Gridin said in a statement on Friday evening. “Det. Gauthier conducted a proper investigation and fully documented the arrest of McArthur so that the information was available to all other investigators.”

Mr. Gridin defended his client’s handling of the interview. “McArthur’s monstrous nature was difficult to uncover because he led a life of extreme deception, not because of anything to do with the 2016 arrest,” Mr. Gridin said. "Det. Gauthier has great sympathy for the victims and the community.”

Constable Allyson Douglas-Cook​, a spokesperson for the Toronto Police Service, said Sgt. Gauthier’s hearing before a police tribunal will be held on Tuesday at 9 a.m.

Inspector Hank Idsinga – the homicide detective who headed the McArthur investigation – has previously said that in the course of his work, he came across “concerning” information. While he did not say what it was, he said he became aware of it after reviewing two previous police investigations into the disappearances of five men from the gay village. All five were later revealed to have been killed.

“I saw something I felt needed to be investigated further,” he told The Canadian Press last spring. He sent a report of his findings to the force’s professional standards unit. The incident happened between the end of the first police probe, Project Houston, in 2014 and the start of the next, Project Prism, in 2017, Insp. Idsinga previously said.

"I think you should take a look at this because we're accountable for what we do," he said he told internal investigators. "I'm not the one to decide whether mistakes are made or not, but I think it's something that certainly needs to be investigated. It was concerning."

Police interviewed Mr. McArthur twice in the years before his arrest in January, 2018. In addition to the 2016 interview, officers talked to him in 2013, after police were told Mr. McArthur had a romantic relationship with Skandaraj Navaratnam, the first man to go missing, and that he had visited his third victim, Majeed Kayhan, before his disappearance. An internal review into the way the 2016 incident was handled was ordered later.

Story continues below advertisement

Mr. Navaratnam and Mr. Kayhan are now counted among Mr. McArthur’s victims, along with Abdulbasir Faizi, Soroush Mahmudi, Kirushna Kumar Kanagaratnam, Dean Lisowick, Selim Esen and Andrew Kinsman. His sentencing hearing for their murders is scheduled to begin on Monday. The case strained relations between police and the city’s LGBTQ communities, prompting questions about how seriously officers took the disappearances, particularly of the men of colour.

The Toronto Police Services Board approved an external review of how its officers handle missing-persons cases last year, but it was not to include the McArthur investigation as the charges were still proceeding through the courts. The head of the review – Justice Gloria Epstein – asked the board this week to lift that restriction.