The King County Medical Examiner has yet to identify the victim, but the neighbor said his name was Hank Lee Sr.
"(Lee has) been living here for the last 34 years and I've been knowing him ever since I've been here," Hank Williams said, adding he's lived there just as long. "Real quiet, peaceful guy."
Williams said Lee lived alone after his wife died about six years ago but family members periodically checked up on him.
But Sunday night, the man called 911 using his medical alert relay service to report he was alarmed by a disturbance outside his home, said Detective Mark Jamieson.
"He was talking about the lights outside and said he had a weapon and wasn't afraid to use it," Jamieson said.
He mentioned a prowler, but there was none, Jamieson said.
The disturbance was the fire department responding to a person in a car who appeared to have some sort of medical crisis in the 6300 block of South Bangor Street.
Additional officers responded to protect the firefighters and an officer at the scene. When they approached the house to talk to the man, he came to the door with a gun, Jamieson said.
The man refused repeated commands to drop the weapon. Jamieson said when the man aimed it at one officer, two other officers fired.
The man died at the scene. No officers were injured. The officers involved were placed on paid leave, which is routine in police shootings.
Williams said everyone in the neighborhood knew of Lee and his battle with dementia.
"It should've came up on (the dispatcher's) screen, indicating all the medical issues he's had up until now," Williams said.
Bob Le Roy, the President and CEO of Alzheimer's Association of Western Washington, says he knows how complicated and terrifying these incidents can become for a patient of dementia or Alzheimer's.
"People with dementia are easily confused and they often mistake friends or family members or police men for intruders," Le Roy said. "They perceive them to be not friends or family but threats."
Le Roy said it can put police officers in a very difficult position.
"It's a very difficult position for them, and of course we want to encourage them and in fact train and support them to recognize the signs and the symptoms they may be dealing with someone with dementia, with Alzheimer's," Le Roy said. "But we certainly can't ask them to put their lives as responders at greater risk... if someone's pointing a gun. The reality of it is: Guns in the home of an Alzheimer's patients are not a good match."