Fourth person charged in Robbie Thomson homicide investigation
A fourth person has been charged in connection with the death of Robbie Thomson, in a case that dates back to his disappearance in 2023.
In an update released Wednesday, April 22, 2026, Lanark OPP say Mark Fenton, 42, of Smiths Falls has been charged with accessory after the fact to murder. This charge has not been proven in court.
Police say he was arrested on April 21, 2026, and remains in custody. He is scheduled to appear before the Ontario Court of Justice in Perth on April 22.
Thomson, who was 34 at the time, was reported missing from the Smiths Falls area in October 2023. Police believe he disappeared sometime between Oct. 12 and Oct. 18 of that year.
This marks the fourth person charged in the case. On Oct. 29, 2025, three individuals were arrested and charged with first-degree murder:
- Christopher Fenton, 48, of Montague Township
- Erin Mackie, 40, of Montague Township
- Joshua Belfiori, 34, of Kingston
Charges have not been proven in court.
Police had previously said that although Thomson’s body had not been located at the time of those arrests, investigators had determined he was the victim of a homicide.
On Oct. 30, 2025, officers executed a search warrant at a property on Kelly Jordan Road in Montague Township, where human remains were later located and identified as Thomson.
The investigation remains ongoing, with police continuing to maintain a presence at the Kelly Jordan Road property in Montague Township.
The Lanark County OPP is leading the investigation, in collaboration with the Smiths Falls Police Service, under the direction of the OPP Criminal Investigation Branch. The investigation has also been assisted by the Office of the Chief Coroner and the Ontario Forensic Pathology Service.
Anyone with information is asked to contact the OPP or Crime Stoppers.