Police have launched a murder inquiry after the bodies of two adults and two boys were found in a house.
Richard and Clair Smith and their children Ben, nine, and Aaron, one, were found in a fire-damaged upstairs bedroom of their house in a cul-de-sac in Pudsey, near Leeds, late yesterday afternoon.
Detectives are thought to be treating it as a case of murder/suicide. No one else is being sought.
Mr Smith, 37, and his 36-year-old wife are thought to have moved into the modern stone-built house a few months ago.
Part of Sheridan Way where the house is located was initially cordoned off amid fears that dangerous chemicals might be present.
Detective Superintendent Paul Taylor of the West Yorkshire Police homicide and major inquiry team said: "Initially, we had concerns regarding the release of harmful chemicals or gases.
"Following testing, we no longer have any concerns with regards to those working at the scene and we will continue our investigations today.
"Inquiries are at an early stage and I would ask anyone with information about the incident to contact the homicide and major inquiry team."
Neighbours spoke of their shock today.
One woman who laid flowers at the police cordon said her children went to school with Ben.
She said: "It's terrible. From what I saw of them, they were very fun-loving, kind and caring - full of life."
The woman, who did not want to be named, said: "They were a nice family."
Another neighbour, who lives round the corner, said: "It's such a shock. We've been up all night watching what's been going on.
"This really is a quiet street. You just don't expect it.
"I didn't know them, apart from seeing them around and about.
"They had two boys. It's just so sad."
The tragedy comes just days after a police officer who had been dismissed by his force attacked his family before apparently killing himself.
Toby Day is thought to have killed his primary school teacher wife Samantha and youngest daughter Genevieve, six, in a frenzied attack at their home just days after he was sacked by Leicestershire Police.
He also attacked their other children Kimberley, 15, and Adam, 13, before taking his own life at their home in Melton Mowbray, Leicestershire, on Thursday.
Police and scientific support officers were still at the Smith family's home today.
The house, which has an integral garage, has a broken lounge window - the only other sign of anything out of the ordinary.
Family friend Sara Turnbull was in tears as she left flowers at the police cordon.
The message on her bouquet said: "You were such a beautiful family. All our love to you. We can't believe you are all gone."
Her husband Dean said the families had known each other for 15 years and been on a number of holidays together.
He said he had not seen Mr and Mrs Smith for a while but bumped into them again recently.
Mr Turnbull said: "We can't take it in. All we know is they are a lovely family, lovely two kids and we're in shock.
"We hadn't seen them for a while but we saw them last week. I went out for a drink a week or so ago and I saw Richard and Clair out.
"I said we'll come round and see you, we haven't seen you for a while.
"We went to their new house and it was superb. Brilliant. We really enjoyed ourselves."
Mr Turnbull said: "There was no sense of any problems."
It is understood that concerned family members discovered the bodies yesterday and chemical concerns were raised after a mystery residue was found on the bedroom wall by police.
Mr Smith worked for a shopfitting firm.
Mr Smith's cousin Gary Tempest said: "It is so unbelievable this has happened.
"They were the perfect family."
Asked whether Mr Smith could have hurt his family, Mr Tempest said: "I don't believe that for a minute.
"He thought the world of them."
He said his cousin was football mad and had no money worries. He said they both had good jobs.
"I've known Richard all my life. There's never been any bad things - arguing or anything."
Friend Sarah Wilson was in tears as she laid flowers.
She said: "I can't imagine what's made this happen, I really can't.
"I just can't believe it, I just can't."
She went on: "They were just ordinary. I'm making that sound like a bad thing, and it's not."
She said she once held Aaron in her arms as her sister was a neighbour, and added: "Such beautiful little boys. Both of them."
Ms Wilson continued: "They were just like anybody else. Just fine.
"There was just no inkling that anything like this would happen. Nothing."