The 26-year-old's baby son, Riley, died on Wednesday.
Police investigating the murder of pregnant
Kelly Mary Fauvrelle in south London have issued CCTV of a man they want to trace.
Detectives wish to speak to a man pictured walking towards the home of Fauvrelle in Thornton Heath and running away from the scene minutes later.
The 26-year-old was eight months pregnant and found with stab injuries at her address in Raymead Avenue in the early hours of Saturday.
She died at the scene, while paramedics managed to deliver her baby son who her family has named Riley.
Police confirmed on Wednesday morning that the baby had since died.
In the footage, released by the Metropolitan Police, a man is seen walking towards Fauvrelle’s address at 3.11am and running back just over 10 minutes later.
Detective Chief Inspector Mick Norman of the Met’s Homicide and Major Crime Command said: “The release of this footage is the next step in what has been a fast-paced, and extremely challenging investigation.
“We need to identify the man shown in the footage urgently, even if only to eliminate him from our enquiries. I need to hear from anyone who knows who he is.
“If this is you, it is imperative that you contact my team immediately.”
He added that the force was unable to say whether Fauvrelle’s attacker was known to her and officers are keeping an open mind.
He said: “A dedicated team of detectives are working day and night on this investigation.
“We have assured Kelly’s family - and I want to assure local residents and the wider public too - that we are doing absolutely everything in our power to find the person responsible.
“I am aware that there is some speculation about whether Kelly’s attacker was known to her. At this stage we simply are not in a position to say and we must retain an open mind.
“One of the key aims of my investigation is to build a complete picture of Kelly’s life and the people with whom she was in contact, but I also need to consider other possible scenarios.
“Members of the public may have useful information, and I am today reiterating my appeal for anyone who may know anything that will assist the investigation to make contact as soon as possible.”
Two men have been arrested on suspicion of murder. One, aged 37, was released under investigation on Sunday, and a second, aged 29, has been released on bail until early August.
Anyone with information is asked to call the police incident room on 020 8721 4005 or Crimestoppers anonymously on 0800 555111.