Neighbours have paid tribute to three members of a "lovely" family found dead after a house fire.
A murder investigation was launched after the deaths of Gary Walker, 57, his wife Caroline, 50, and their daughter Katie, 24 on Sunday.
They were pronounced dead at the home in Stuarts Close, Hemel Hempstead, Hertfordshire, at about 12:30 BST.
Police said they believe it was an isolated incident.
The family have not been formally identified but were named by neighbours.
One said: "They were a lovely family. They had been here for about 30 years. It is a terrible tragedy. We don't know what happened."
The alarm was raised by neighbour Peter Downer, who described seeing smoke coming from their house.
He said Mr Walker was a draughtsman, while his wife worked at a supermarket and their daughter worked with animals. The couple are believed to have had another son and daughter.
Forensic officers continued to work at the house on Tuesday, with Stuarts Close cordoned off and a blue police tent erected in the garden.
Det Insp Iain MacPherson of the Bedfordshire, Cambridgeshire and Hertfordshire Major Crime Unit, said "all possible motives" were being considered.
"We are dealing with three suspicious deaths and are not looking for anyone else in connection to this incident at this time," he said.