Flags in Quebec are flying at half-mast today to mark 24 years since the mass shooting at the École Polytechnique in Montreal that left 14 women dead.

On Dec. 6, 1989, a man entered classrooms at Polytechnique, as it's known in Montreal, and forced the male and female engineering students to separate. He then shot the women with a semi-automatic rifle.

The Polytechnique victims

Geneviève Bergeron.
Hélène Colgan.
Natalie Croteau.
Barbara Daigneault.
Anne-Marie Edward.
Maud Haviernick.
Barbara Maria Klueznick.
Maryse Laganière.
Maryse Leclair.
Anne-Marie Lemay.
Michelle Richard.
Sonia Pelletier.
Annie Saint-Arnault.
Annie Turcotte.

Heidi Rathjen was at Polytechnique on the day of what has come to be known as the Montreal Massacre. She was hiding in a classroom that the gunman didn't enter.

The anniversary of the shootings is particularly painful for her and other gun control advocates since the federal government dismantled the long-gun registry in 2012.

"It was devastating. We have to keep fighting. Luckily we have a chance to keep that cornerstone of gun control in Quebec. We're not going to stop fighting until we get registration back one day," she says.

Polytechnique informed Canada's gun control laws

Rathjen co-founded the Coalition For Gun Control in the wake of the massacre, and has fought for gun control laws for over two decades.

Her group lobbied the Canadian government for gun control laws, with the first steps taken in 1990 when then Prime Minister Kim Campbell introduced Bill C-80. That bill died, but a year later was replaced with a revised version, Bill C-17, which eventually passed.

In 1993, Campbell's successor Jean Chrétien, brought in the long-gun registry.

Shortly after the dismantling of the federal long-gun registry was announced in 2012, Quebec filed an injunction to preserve the province’s data for the eventual creation of its own registry.

After several roadblocks — including a Quebec Court of Appeal decision in June to not force the federal government to preserve the data — Quebec won an appeal this month to the Supreme Court of Canada.

Survivors of the Montreal Massacre and people touched by the events of Dec. 6, 1989, assemble every year to mark those events and remember the victims.

At 12:30 p.m. ET, people will gather outside the Montreal courthouse after 14 white roses are laid at the École Polytechnique memorial plaque.