Investigators are weeks away from revealing why there was live ammunition in a Florida police officer's gun when he fired and fatally shot a retired Twin Cities librarian during a Citizens Academy role-playing exercise, authorities said Thursday.

Punta Gorda Police Chief Tom Lewis revealed little else while reading a statement to the news media in the small city on the southern Gulf Coast of Florida, where Mary Knowlton, 73, was shot in front of her husband of 55 years during the demonstration.

Smith said the "shoot-don't shoot" demonstration has been carried out safely by his department for the past two years and has been conducted successfully by other law enforcement agencies for many years.

"Something went terribly wrong," Lewis said of the killing Tuesday evening at police headquarters. "I accept full responsibility for my department [and] my officers."

In the meantime, investigators with the Florida Department of Law Enforcement are anywhere from two to four weeks away "from concluding anything," Lewis said.

Mary and Gary Knowlton, who had lived in Prior Lake for many years, were among 35 academy participants at police headquarters when Knowlton and one other person were chosen for the "shoot-don't shoot" role-playing exercise that involves decisions about when to use lethal force.

The officer, identified as 28-year-old Lee Coel, shot Knowlton in what the chief has called a "horrible accident." She died at a nearby hospital.

"All I remember [is] it being really loud and thinking, 'Wow, I didn't expect that to be that loud,' " said John Wright, Punta Gorda Chamber of Commerce president, who described to WINK-TV of Fort Myers what he witnessed.

"She didn't go down straight away, so there was an element that thought, 'OK, she's playing.' But she wasn't and when she turned, I could see in her eyes that this was bad, this was not going to end well. When she hit the ground, that was just when the shock factor hit us all."

Police say Knowlton assumed the role of a police officer. Photographs published by the Charlotte (Fla.) Sun showed Knowlton with a blue plastic gun and Coel decked out as a "bad guy" in a hoodie and mask. Both hands clutched the silver revolver as he's about to fire the fatal round.

One of the Knowltons' sons, Steve, told the Associated Press from the family's Punta Gorda home that the class was supposed to be "a fun night" for his parents. He said his father is "devastated" by what happened before his eyes.

The officer who fired the lethal shot joined the force on March 17, 2014, and "is frequently seen throughout our community providing department presentations and tours and specifically role-playing in these shoot-don't shoot scenarios as well as a police presence at youth and neighborhood events," the department said in a statement late Wednesday.

Coel remains on administrative leave during the investigation into how the revolver, which is not a service weapon and has been used in previous training situations, became loaded with lethal ammunition.

"We were unaware that any live ammunition was available to the officer," Lewis said during a news conference Wednesday afternoon. "We believed that [for] the particular caliber of the weapon used, that there were only blank rounds available to the officer,"

The Fort Myers TV station also reported that Coel was the subject of an excessive force complaint in October that resulted in no discipline, and he had two similar complaints filed against him in 2013 while with the Police Department in Miramar, Fla., prompting him to lose his badge for a time before he resigned for failing to satisfactorily complete a field training program.

In his statement to the news media Thursday, Chief Lewis acknowledged the complaint from last fall but would only say that it's the subject of "civil litigation." Lewis did not address the complaints against Coel in Miramar.

Steve Knowlton said he will forgive the officer who fired. "I obviously can't say it's easy to forgive, but it needs to be done," he said. "I forgive him."

Before retiring, Mary Knowlton was the librarian at Parkview Elementary School in Rosemount from 1988 to 2004, then was a substitute librarian at other schools in the Rosemount-Apple Valley-Eagan district through 2013. Knowlton also worked for the Scott County Library in the 1980s at the Prior Lake branch before taking over at Parkview.

The Knowltons relocated to Punta Gorda from Prior Lake, where they had lived since 1973.

Mary Knowlton originally was from Austin, Minn., where she went to high school and graduated in 1961. She then studied at St. Olaf College, the University of Minnesota and Minnesota State University, Mankato, among other institutions.

Punta Gorda, a city north of Fort Myers with a population of roughly 16,000, describes its Citizens Academy as a free eight-session course of interactive classes "designed to give citizens an up-close and personal look at how city government functions and helps shape our community."