Yoon, who is about 24 years old, was sentenced to two years in prison in the summer of 2012.
The information came to CBC News from those who have spoken with Yoon. The charges against him were described by one source as "the usual charges for terrorism."
It appears Yoon had no role in the Algerian gas plant attack by militants linked to al-Qaeda in January of this year, in which his two former classmates, Ali Medlej and Xris Katsiroubas, were killed. When the attack happened, Yoon was already behind bars in Mauritania
Before his arrest, Yoon attended a religious school in Mauritania, reportedly with Americans and Europeans, studying the Qur'an. Yoon, was raised a Catholic, but he converted to Islam a year before graduating from London South Secondary School.
- Friend of Canadians in Algerian attack studied religion in Africa
Amnesty International is not campaigning or commenting on Yoon's behalf because he asked the organization not to.
The RCMP confirmed Thursday that the remains of Medlej and Katsiroubas were found at the site of the attack on the Algerian gas plant.
CBC News has learned that RCMP in London were asking questions about the three men in June 2012, seven months before the Algeria attack.