The man shot his partner and two other relatives before killing himself was not depressed the detective leading the murder inquiry has said, leaving the motive for the crime unclear.
Taxi driver Michael Atherton, 42, blasted Susan McGoldrick, 47, her sister Alison Turnbull, 44, and her daughter Tanya Turnbull, 24, on New Year's Day at his home in Horden, Peterlee, County Durham.
Detective superintendent Paul Goundry, speaking to reporters after inquests were briefly opened, said Atherton's doctor had seen no evidence he was suffering from any mental illness or depression.
"The focus of my investigation has to be why did a minor domestic argument turn into this tragedy?" he said.
The killings are not believed to have been premeditated as he had made an arrangement with a friend to hunt rabbits the following day.
Mrs McGoldrick's daughter from a previous relationship Laura, 19, was hit by the spray of shot aimed at her mother. She ran upstairs and escaped through a window with her boyfriend.