The father of a missing Toronto teen says stress over his loss led to him stabbing three people, including a couple who had once acted as his sureties.

Vakhtang Makhniashvili, 51, will be sentenced on July 26 after pleading guilty earlier this week to three counts of aggravated assault.

The charges stem from the stabbing of a former neighbour in May 2010 and the November stabbings of David and Delores Langer, a couple who had stepped forward to post bail for the previous attack.

Makhniashvili, a Georgian immigrant, was thrust into the public eye when his daughter Mariam Makhniashvili disappeared without a trace from outside her Forest Hill-area high school.

Mariam, then 17 years old, and her brother had arrived in Toronto from Georgia to reunite with their parents just weeks before her disappearance.

Despite an exhaustive search, Toronto police have never been able to determine what happened to the teen.

On Friday, an agreed statement of fact was read into during a brief court appearance.

He says he stabbed his 26-year-old neighbour in May 2010 after accusing him of being responsible for his daughter's disappearance.

He also said he stabbed the Langers after blaming them for an unfavourable newspaper article about his family.

Makhniashvili's lawyer, Calvin Barry, said he would be asking for a sentence of two years less a day.

Last November, Makhniashvili's 17-year-old son George, the last to see Mariam before her disappearance, vanished from home.

He turned up unharmed at a police station the next morning.

George and Mariam came to Toronto in June 2009 from the Republic of Georgia to reunite with their parents, who had spent the previous five years working in the United States.

With files from CTV Toronto's Austin Delaney