Charles A. Hamilton (Courtesy Fairfax police)

Charles A. Hamilton, 59, was arrested after officers responded to a report of a person shot at a single family home in the 11300 block of Geddys Court around 9:40 a.m., police said.

Officers found Hamilton’s sister Ruth Allen, 68, of the 2000 block of Durand Drive in Reston, suffering from a gunshot wound, police said. Allen was transported to the hospital, where she died.

Police declined to discuss a motive for the shooting. Allen’s husband said in an interview that it arose from a dispute over the care of another sibling who had recently suffered a stroke.

Allen and Hamilton had been discussing guardianship of the sibling when the conversation grew heated and Hamilton pulled out a gun and shot his sister, George Allen said.

Their mother was also at home at the time, George Allen said.

Ruth Allen had recently retired as an environmental epidemiologist with the EPA and had served on the faculty of American University. She had served as adjunct faculty at Yale University, where she received a PhD.

“Ruth was a very giving person,” George Hamilton said. “I keep telling people this is what happened. It’s like a bad movie. I keep thinking I will be able to change the channel.”