The shooting of a woman in a house in Liverpool which was then set alight was a "targeted attack", police have said.
Police do not know why Lucy Hargreaves was targeted
Lucy Hargreaves, 22, a mother of three, was shot at her home in Lambourne Grove, Walton, before petrol was used to set the house on fire.
Ms Hargreaves' 28-year-old partner and their two-year-old daughter escaped from the fire on Wednesday.
Merseyside Police said on Friday they were unsure of a motive and want those with information to get in touch.
Detectives believe that three men were involved in the murder, with one or two going into the living room and shooting Ms Hargreaves, before starting the fire.
A grey Lexus estate car is also being linked to the attack. It was stolen a week before the murder and was found burnt out on Wednesday.
Ms Hargreaves' partner was asleep upstairs and heard noises in the house, before seeing the fire in the hallway.
He escaped through an upstairs window with the child. Several attempts were made by him and neighbours to pull Ms Hargreaves from the burning house.
Det Ch Insp Ian Mulcahey said the murder was a "targeted and localised" attack.
He added: "This was a deliberate and particularly brutal attack on a young woman, which has denied three children a mother.
"Why anyone would take such appalling actions against her is unclear and defies human nature.
"Her family is devastated and I would urge anyone who has information to come forward.
"I am particularly interested in talking to anyone who saw anyone acting suspiciously outside the address in Lambourne Road before the attack at the house."
Ms Hargreaves has two other children who were not at home at the time of the fire - two boys aged three and five.
A statement from her family said Ms Hargreaves was a "wonderful and thoughtful daughter and sister".
It added: "She was happily bringing up her children and making the most out of life when this brutal slaying took place."