A Washington County deputy kneels while finishing the scene investigation on Monday, May 2, 2011, following a homicide at 1355 Deer Run Drive in Riverside. Washington County authorities have arrested and charged Thomas Hansen with first-degree murder after he allegedly shot Sharon Gerot while she was riding the lawnmower in a field adjacent to the house they shared. (Liz Martin/The Gazette)

A retired Johnson County official charged with fatally shooting his female companion after a domestic dispute has pleaded not guilty.

Online court records show Thomas Lee Hansen of Riverside entered a written not-guilty plea last week to one count of first-degree murder in the death 54-year-old Sharon Gerot.

Thomas Hansen

A criminal complaint accuses the 70-year-old Hansen of shooting Gerot on May 1 with a semi-automatic handgun while she was riding a lawn mower in their backyard. Authorities say the two had lived together for years but had been arguing earlier in the day. They were planning to go work at Yellowstone National Park.

Hansen retired as Johnson County’s emergency management coordinator in 2007. Before that, he had worked for the Iowa City Fire Department.

Trial has been scheduled for Jan. 24.