It is not every day that a dog lies in state under the dome of a capitol.

But Gilbert, a 4-year-old golden retriever who belonged to the family of State Representative Melissa Hortman of Minnesota, was no ordinary dog.

Gilbert was killed on June 14 after a man stormed into Ms. Hortman’s home and opened gunfire, also killing Ms. Hortman and her husband Mark. It was one of two shootings of state lawmakers that the man, identified by investigators as Vance Boelter, carried out that day, prompting what officials called the state’s largest manhunt.

On Friday, all three lay in state at the Minnesota Capitol. Ms. Hortman is the first woman in the state to receive the honor, her husband is the first who wasn’t a public official or veteran, and Gilbert is the first animal.

To understand why Gov. Tim Walz of Minnesota saw fit to include Gilbert in a remembrance honor that fewer than 20 state dignitaries have received, it helps to go back to 2014, the beginning of the Hortman family’s yearslong passion for training service dogs.

The Hortmans’ daughter, Sophie, who was then a senior in high school, decided to train a service dog for a school project and brought Minnie, a black Labrador retriever, into the family.

Sophie and Mr. Hortman put Minnie through a rigorous training program run by Helping Paws, a nonprofit that provides service dogs to people with disabilities, including veterans and emergency personnel. In July 2016, Minnie was paired with Aric Elsner, an Air Force veteran with chronic pain and post-traumatic stress disorder.