AUSTIN — On Monday the clock stops on the University of Texas tower.

The 24-hour observance will mark the 50th anniversary of the day that UT engineering student Charles Whitman climbed to the top of the Main Building, fatally shot 16 people, wounded another 32, and opened a new chapter in the history of mass murder.

Software developer Louise Nelson, who works in the tower, thinks about his rampage.

“As I walk across campus, I think about where I would hide,” she said.

Whitman died on the tower, but his attack and the response by armed civilians still reverberate.

Come Monday, as Texans pay tribute to the casualties of that day’s shooting, they also will begin to legally carry concealed handguns on college campuses, including UT Austin.

A year after it was signed into law, campus carry remains controversial, as does the symbolism of its arrival.

U.S. Rep. Lloyd Doggett, a UT student in 1966, is scheduled to speak Monday at a commemorative ceremony.

“Campus carry was imposed on our public universities over the objection of students, faculty, administrators, and survivors of the Whitman shooting,” said Doggett, a Democrat whose district includes parts of Austin, in an email.

He called it “cruel irony” that the policy is implemented on the anniversary of the first mass shooting on a university campus.

“Campus carry would not have helped then, and it only offers added danger now,” he said.

As Whitman picked off victims – as far as 500 yards away from his perch on an open observation deck – UT students quickly returned to campus with rifles and opened fire on the tower.

An employee at the campus bookstore got a gun and, along with two police officers, went to the top of the tower to confront the killer.

In testimony last year, Claire James, then a pregnant student whose unborn child and boyfriend were killed by Whitman, told Texas lawmakers that the armed civilians shooting at the tower were keeping emergency crews from helping her.

Nelson said armed civilians just become “additional targets” during a campus shooting.

“It makes it very difficult for law enforcement to determine who’s doing what,” Nelson said. “I don’t buy the argument that a good guy with a gun will always prevail.”

But that idea – of allowing gun owners to protect themselves and others – was the strong sentiment of lawmakers who passed campus-carry after years of debate. Gov. Greg Abbott signed the law last summer.

Molly Farr, 27, who will be a sophomore English major at UT this fall, was visiting campus on Thursday with her mom and her two children.

They stopped to watch the turtles in the pond next to the site where workers installed a stone inscribed with the names of Whitman’s victims. They planned to visit the tower.

Farr said she has a gun permit, might carry a weapon on campus, and isn’t afraid of being caught in a crossfire.

“Why not?” she said. “Especially with everything going on in the world.”

Zach Brust, a first-year MBA student who graduated from the University of Florida, just moved to Austin and said carrying a gun is “not my style.”

The shooting wasn’t on his mind, and the notion that armed student or faculty member could bring down a sniper struck him as unlikely.

“I feel like that’s an extreme outlier,” said Brust, 27.

Lee Senter, 21, an accounting major from San Antonio, was also dubious.

“The hero in everyone would want to do something,” Senter said. “Realistically, everybody would just want to find a place to hide.”

Joe Zych, a bearded 26-year-old bartender and Boston transplant, said he’s aware of the possibility that somebody might open fire on a campus.

And he said he is “generally in favor of the rights of citizens, even if freedom increases danger slightly in our day-to-day lives.”

But Zych, who was visiting a friend on campus, said he doesn’t plan to get a gun.

“I hope to live a life where I never have to fire one,” he said. “You don’t need people like me grabbing weapons.”

Nelson, the software developer, said whether she carries a gun is “nobody’s business but mine.”

As she stood outside the Main Building, facing the place where Whitman rained down fire and triggered a national debate, she reflected on what happened 50 years ago and what will change come Monday.

“This is a very representative moment,” she said. “We’re living through history.”

John Austin covers the Texas Statehouse for CNHI’s newspapers and websites. Reach him at jaustin@cnhi.com.