The family of a heavily pregnant woman who was stabbed to death her bedroom in south London were woken by her “screams”, police have said.
Kelly Mary Fauvrelle, 26, who was eight months pregnant, died in the early hours of Saturday and her baby Riley was pronounced dead on Wednesday.
Det Ch Insp Michael Norman said Ms Fauvrelle was the victim of a “sustained and vicious attack”.
He said police were yet to establish a motive for the “double homicide”.
The Met has also released CCTV which shows a figure walking towards Ms Fauvrelle’s home at about 03:15 BST on Saturday, then running away just over 10 minutes later.
Det Ch Insp Norman, from Homicide Command, said whole Ms Fauvrelle’s family – her mother, two brothers, sister and sister’s baby son – were in the house on Raymead Avenue, Croydon, at the time of the attack.
“The family were alerted just before 3:30 in the morning by the sound of screams which was clearly Kelly,” he said.
“Kelly’s sister was the first person to go into the room, by that point there was no-one else there.”
He said police and paramedics did “everything they possibly could to try to save Kelly’s life and it was clear they were going to be unsuccessful” and then delivered the baby by Caesarean section.
Ms Fauvrelle was pronounced dead at the scene and the baby – named Riley by the family – died in hospital.
Det Ch Insp Norman said “we have to remain open minded” regarding a motive to the attack and there is a “need to build as complete a picture of Kelly as we possibly can”.
He said that Ms Fauvrelle’s bedroom was at the rear of the ground floor and there was a communal passageway so “potentially the obvious access point would be through the kitchen”.
“There is no sign of a forced entry but that does not mean, through accident, the premises were insecure,” he added.
Police said Riley’s father was not currently being treated as a suspect.
Local MP Steve Reed raised the murder in Parliament during Wednesday’s Prime Minister’s Questions and said: “The police now believe this may have been a random attack by someone unknown to the family.”
In response, Prime Minister Theresa May said “we were all shocked when we saw this terrible act”.
A 37-year-old man arrested on suspicion of murder has been released with no further action, while a 29-year-old man held over the same offence was bailed until a date in August.