The verdict was reached after five hours of deliberations.
John Leonard MacKean was facing charges of sexual assault and communicating for the purpose of obtaining sexual service from a person under 18.
Crown lawyer Lloyd Tancock says the guilty verdict will mean jail time for the 64 year old.
However, Tancock told reporters it's too early to discuss the prison term the Crown will seek.
MacKean is the third and final person charged in the confinement and sexual assault of a teenage boy in Upper Chelsea in September 2012.
Wayne Cunningham died while on the run from police in Northern Ontario while David Leblanc is serving an 11 year jail term for his role in the crime.
MacKean will be sentenced on June 24th.
