A mother and her two young children found dead in their Pudsey home all suffered stab wounds, reportedly inflicted by their father wielding a knife against his "perfect family".
Clair Smith and her one-year-old son Aaron were killed by a single stab wound to the chest, while nine-year-old Ben died from suffocation, police have confirmed. Father Richard Smith is thought to have killed his family and later died from smoke inhalation.
The "gruesome discovery" of the four bodies at their house in Sheridan Way, Leeds was made after concerned relatives raised the alarm.
Clair's parents, Alan and Norma Smith released a statement describing her as "an exceptional person, loving and caring to everyone".
"She was a loving mum, her children were her life, and everything centred around her family and home. She was our daughter and our best pal.
"We cannot imagine what caused this tragedy", she added.
Detective Superintendent Paul Taylor said police were working on establishing the facts "leading up to the tragic event that has ended the lives of four people and a seemingly happy family".
"Ben's advent calendar is not opened on the Saturday so we believe something's happened overnight Friday or the early hours of Saturday but, of course, if anybody else has any information that would contradict that we would very much want to hear from them," he said.
"The coroner must rule on what happened that night or over that weekend. You can draw conclusions on what I've said if you wish, but I'll be putting a file to the coroner."
The detective said he did not want to "go into" possible motives.
"What the state of mind of Richard, Clair or anybody else was will be a matter we'll be trying to investigate.
"It's not for me to guess now."