Police are looking to identify a man caught on camera walking towards the address of a murder victim and running away from the scene minutes later.
Kelly Mary Fauvrelle, 26, was eight months pregnant and found with stab injuries at her address in Raymead Avenue, Thornton Heath in South London in the early hours of Saturday.
Paramedics managed to deliver her baby son, but he died in the early hours of this morning, Scotland Yard said.
Police released footage showing a man walking towards the address and running away 10 minutes later
In the footage released by the Metropolitan Police, a man is seen walking towards Ms Fauvrelle's address at 3.11am and running back just over 10 minutes later.
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.
Detective Chief Inspector Mick Norman of the Met's Homicide and Major Crime Command said: "This morning, we heard the sad news that Kelly's baby son, Riley, has died in hospital. Our thoughts remain with their family.
"This tragic development makes it even more important that anyone with information comes forward as a matter of urgency.
"We have released footage as 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 inquiries. 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 Ms 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."