Just days after Jeremy Steinke was arrested in the killing of a Medicine Hat couple and their young son, the 23-year-old told police that he participated in the slayings because he wanted to “impress” his 12-year-old girlfriend, who was the mastermind behind the plot to murder her family.

Jurors in the Court of Queen’s Bench in Calgary took 11 hours to convict Mr. Steinke, now 25, of three counts of first-degree murder in the April, 2006, deaths of an eight-year-old boy and his parents. The couple’s daughter, known in court as J.R., was convicted last year on the same set of charges. Neither she nor her family can be identified under the Youth Criminal Justice Act.

In the weeks leading up to the slaughter of a Medicine Hat family, Jeremy Steinke exchanged e-mails planning the murders not only with his underage girlfriend – whom he describes as the mastermind of the plot – but also with two unnamed friends, an Alberta court was told yesterday.

Many of the Internet musings and exchanges were presented during the girl’s trial last year, when she was convicted of three counts of first-degree murder. But new e-mails were made public yesterday at the Court of Queen’s Bench in Calgary, where Mr. Steinke is facing the same set of charges.

An Alberta judge has sentenced Canada’s youngest convicted multiple murderer to 10 years – the maximum allowed for someone her age – for the slayings of her mother, father and eight-year-old brother.

A Medicine Hat girl may have made Canadian legal history by being the youngest person ever convicted of multiple murders.