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 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, who wasn't identified, 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 Wednesday. “The officer involved is grief stricken.”

Mary Knowlton, a 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.

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

The younger Knowlton said Wednesday at his parent's home that, on his mother's behalf, he was forgiving the officer who fired the gun.

“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.”

Officer Oscar Vasquez of the Jacksonville, Ill., 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 non-lethal devices, he said.

“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.

Mary Knowlton moved to Florida after living in Minnesota.