DALLAS—The University of Texas at Austin on Monday held a solemn commemoration of a dark history: the 50th anniversary of the school’s clock tower massacre, when a sniper shot more than 40 people, drawing back the curtain on an era of modern-day mass shootings.

As the school recalled its bloodiest day, a new state law also went into effect Monday that allows concealed handguns on public university campuses.

“It is unfortunate timing,” said J.B. Bird, a university spokesman. “These two events are completely unrelated, and we’re keeping them completely separate.”

While the law took hold for the first time, the school unveiled a memorial to the victims and survivors of the 1966 shooting, where Charles Whitman, a troubled ex-Marine, climbed to the observation deck of a 307-foot clock tower and sprayed the campus with gunfire before being killed by police. And survivors of the rampage, which killed 17 people, spoke of what happened that sweltering summer day.

“The violence that seized this campus began in the heart of one,” said Claire Wilson James, who was shot in the attack and lost her unborn child. “Let this memorial remain on this campus and in our minds as a reminder of the power we have…to become a community of love.”