After he murdered a student from another school at his home on Oct. 27, 1975, the perpetrator opened fire on his religion class at Ottawa's St. Pius X High School, wounding 18-year-old Mark Hough. Hough died in hospital just over a month later. Five decades later, his family is opening up about what happened next.

Warning: This story discusses school violence, sexual assault and suicide.

For decades, the family of an Ottawa student killed in a historic high school shooting has largely kept their memories of that traumatic time in what one sister calls "the memory box."

Now, as the 50th anniversary of his tragic death approaches, the contents of that box are spilling out.

On Sunday, the family of Mark Hough — who never made it to his 19th birthday — will meet on the west side of Ottawa's Rideau Canal and gather around a simple wooden bench they had dedicated to him earlier this year.

The memorial is an acknowledgement of Hough's life, his sister Lynne McArthur says. But it's also a reminder that "bad things can happen anywhere, even in Ottawa."

Earlier this year, Hough's family had a bench along Ottawa's Rideau Canal dedicated to Hough. The family will gather there on the eve of the shooting's anniversary. (Guy Quenneville/CBC)

On Oct. 27, 1975, Hough and several other students in a packed religion class at St. Pius X High School were shot by a deeply troubled classmate who had raped and murdered Kim Rabot, a girl from a different school, at his home earlier that day.

With the exception of the gunman, who took his own life, every other victim of the classroom attack — one of Canada's first school shootings — survived.

But Hough died over a month later in hospital, bringing the day's total death toll to three.

" From the moment I found out that Mark died, I put him out of my mind because it was too painful to do otherwise," McArthur says.

'I remember when his classmates came to our house, one of them, Doug Boyd, said to me, "He was too good for this world." I have always remembered that ray of light,' Hough's sister Lynne McArthur