ST. PETERSBURG — Pinellas County Sheriff Bob Gualtieri now supports arming teachers and other school personnel as a line of defense against school shootings, a striking change of heart driven by his work with a state commission investigating February's massacre at Marjory Stoneman Douglas High School.

Gualtieri said Friday he changed his mind after watching surveillance video and studying the timelines of Parkland and other school shootings as chairman of the commission established to review what went wrong and recommend ways to make schools safer.

The man accused in the shooting at the Broward County school, Nikolas Cruz, paused to reload his gun five times — moments that could've been taken advantage of by trained volunteer teachers and school staff had they been armed, Gualtieri said. A school resource deputy stayed outside while Cruz sprayed bullets from an AR-15 rifle inside, investigators said. The final fatal rounds had already been fired by the time law enforcement officers arrived.

"The schools across Florida need a change in their culture," Gualtieri said. "Yes, those teachers are great people doing great work and they need to be able to teach, but you can't teach dead kids. Safety has to come first."

The idea of a statewide program to arm teachers arose in the wake of the Valentine's Day shooting that killed 14 students and three staff members. Amid fierce opposition, lawmakers pushed through a sweeping school safety package that allowed school faculty members other than full-time teachers to carry weapons on campus.

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The idea is opposed by the state teachers' union as well as the teachers' union in Gualtieri's own county.

Mike Gandolfo, president of the Pinellas Classroom Teachers Association, said Friday he believes security should be left to sworn police officers or sheriff's deputies and that guns in classrooms would only put more strain on overworked teachers.

"I would feel safer knowing that a trained law enforcement is the person protecting us," Gandolfo said.

Gualtieri, too, once held that opinion.

In Tampa Bay and across the state, school boards came to realize that the financial and human capital it would require to place a sworn officer in every school was impossible with the funding and time restraints handed down by the Legislature.

Gualtieri estimated the figure statewide at $400 million.

Pinellas opted instead to staff most schools with armed guards. Dozens of guards went through 176 hours of training over the summer, including active shooter drills and firearms training. Hillsborough and Pasco went similar routes, while Hernando is staffing with school resource deputies.

But one guard per school, or even more than one in selected high schools, isn't enough, Gualteri said.

He pointed to the enrollment and footprint of Stoneman Douglas High: 3,300 students and 200 staff across a 45-acre campus with 16 buildings.

The additional fire power from teachers trained to carry weapons would provide more coverage and create a deterrent that would make potential attackers think twice, Gualteri said.

Based on interviews with Stoneman Douglas teachers, the commission received a recommendation last week that willing teachers and other school staff be allowed to carry arms, he noted.

"Those that want to go through a rigorous selection process," he said, "those who want to volunteer for it, those who have the courage to do it, the willingness to do it — why would we not give them the opportunity?"

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Still in question is whether arming teachers will make it into a report of findings and recommendations the commission will submit to state leaders by Jan. 1.

Gualtieri emphasized his position is a personal one. He believes it is worth a serious discussion by the commission.

At least one fellow commission member, Polk County Sheriff Grady Judd, has long been a proponent of arming teachers.

The idea drew a range of concerns from school boards, teachers and teachers' unions.

A month after the shooting, Pinellas County School Board members voiced unease over questions of liability and the potential emotional impact on students. Black lawmakers worried how it would affect students of color, who already face bias and discipline disparities in schools across the state.

Even Republican Gov. Rick Scott opposed the idea.

The Pinellas union's Gandolfo said he'd rather see more funding for mental and emotional health counseling in the schools, hardened buildings and sworn law enforcement on campus.

Still, Gandolfo said he agrees with Gualtieri on one point: It's not if, but when, another attack happens.

With that in mind, Gualtieri said, the key is lessening the impact.

"The status quo has failed," he said, "and unless we make change, we will continue to have an environment that doesn't provide the right level of safety in schools."

Information from the Associated Press was used in this report. Contact Kathryn Varn at (727) 893-8913 or kvarn@tampabay.com. Follow @kathrynvarn.