A former Iowa City Fire Department battalion chief and also former Johnson County director of emergency management has been accused of killing his longtime companion.

Riverside resident Thomas Lee Hansen, 70, was arrested and charged with first-degree murder after he allegedly shot and killed 54-year-old Sharon Kay Gerot, the woman with whom he was living.

Following an argument, Hansen allegedly shot Gerot from behind while she was riding a lawnmower behind their Riverside home Sunday, a police complaint said, according to the Associated Press.

Johnson County Supervisor Pat Harney, who said he’s known Hansen for nearly 40 years, said he does not understand what would have caused Hansen to kill Gerot.

"You never know what’s going through someone’s mind or what he’s going through," he said. "It just seemed so out-of-character for him."

Authorities were notified of the shooting at 3:43 p.m. Sunday. When investigators arrived on scene, they found Gerot lying on the ground. She was pronounced dead at 4:40 p.m., according to a press release from the Washington County prosecutor.

Hansen and Gerot were planning on leaving Riverside to work at Yellowstone National Park later this month, where Hansen planned to work as a seasonal laborer and Gerot as a biological science technician, the AP reported.

Those who knew Hansen are surprised, Johnson County Supervisor Terrence Neuzil said.

"I’ve seen the pictures … and that’s the guy I used to work with," Neuzil said.

Harney described Hansen as an outgoing individual — business-like — who did a good job training and coordinating for Johnson County.

Neuzil said that although he didn’t not know Hansen very well, they worked closely together for Johnson County.

"He had a calm demeanor, and he was someone who was extremely approachable," he said. "Anybody who knows him is absolutely in shock that he would resort to this type of violence."

Hansen was a city official for more than 40 years, first serving as an Iowa City firefighter and then later achieving rank of battalion chief, the supervisors said. He then became the Johnson County director of emergency management and served when the 2006 tornado hit Iowa City.

Neuzil said if the charges prove true, he will be disgusted.

On Monday, Hansen made his initial court appearance and did not enter a plea at the hearing.

District Judge Lucy Gamon set Hansen’s bail at a $2 million, cash-only bond, according to the AP.

"A criminal charge is merely an accusation, and the person charged is presumed innocent until and unless proven guilty in court," the press release said.

Officials at the Washington County jail are currently holding Hansen and officials are awaiting the results of Gerot’s autopsy.

"If he indeed took the life of another human being, that is a sad day for everybody," Neuzil said.