PUNTA GORDA, Fla. —A police “shoot/don’t shoot” demonstration in Florida went shockingly awry when an officer shot and killed a 73-year-old former librarian with what police said was real ammunition used by mistake at an event designed to bring police and the public together.

Authorities didn’t immediately say how a gun with a live round came to be used at Tuesday evening’s demonstration, noting blank rounds are typically used in such classes. The officer has been placed on administrative leave, and the Florida Department of Law Enforcement is investigating.

“We were unaware that any live ammunition was available to the officer,” Punta Gorda police Chief Tom Lewis said at a news conference Wednesday. “The officer involved is grief stricken. We’ve got officers assigned to him to make sure he’s psychologically stable.”

Mary Knowlton, a well-known community volunteer, was shot after being randomly selected to take part in the role-playing scenario illustrating the split-second decisions an officer must make about firing. It was part of a popular citizens academy attended by 35 people, including her 75-year-old husband, and the police chief.

Her son, Steve Knowlton, said his father was “devastated.”

The younger Knowlton said in an interview Wednesday at his parents’ home that, on his mother’s behalf, he was forgiving the officer who fired.

“There’s too much hate in this world, in America, we always feel like we need revenge and it doesn’t solve anything,” he said. “I obviously can’t say it’s easy to forgive, but it needs to be done. She’s watching me now.”

Punta Gorda police Lt. Katie Heck said officers in such demonstrations normally use “simunition guns,” which are real-looking weapons that fire a nonlethal projectile with reduced force. But Knowlton was mistakenly struck with a live round, officials said.

Later Wednesday afternoon, Heck identified the officer as Lee Coel and said he has worked for the department since 2014. She said Coel frequently gave department presentations and tours, “specifically role-playing in these shoot/don’t shoot scenarios.”

The class put on by the Chamber of Commerce and the Punta Gorda police station, was just one stop during the weeks-long curriculum.

Officer Oscar Vasquez of the Jacksonville (Illinois) Police Department, who is president of the National Citizens Police Academy Association, said he had never heard of anyone taking part in such courses being fatally shot. He said most departments do not use weapons in “shoot/don’t shoot” scenarios that are capable of firing a live round.

“When we run scenarios, we will use starter pistols,” Vasquez said. “You can’t even put live ammunition in them.”

Some departments use video simulators or other nonlethal devices, he said. Officers involved in most citizen academies don’t typically even bring service weapons into classes, he added. Citizens are told beforehand that live weapons won’t be used.

“We put them in the shoes of the officers so they can see, real time, the decisions we have to make and the time frame we have to make them.”

With suspicions running high between police and many citizens in recent years, particularly in minority communities, Vasquez said, a death like the one in Punta Gorda is extremely unfortunate.

“It just breaks my heart. It’s such a tragedy,” he said.

Mary Knowlton attended the class with her husband and it was supposed to be “a fun night,” her son said.

Steve Knowlton said Wednesday that he used to tease his mother about how much she worked in retirement. She helped with the local Chamber of Commerce, was active in a program for at-risk kids, loved the library and spent hours there volunteering.

She moved to Florida from the Minneapolis-St. Paul area.