Video report by ITV News Correspondent Juliet Bremner
The brother of a mother-to-be who was stabbed to death in south London has paid tribute to the "beautiful person" who "couldn't have been a better sister".
Kelly Mary Fauvrelle, who was around eight months pregnant was stabbed to death at a home in Croydon on Saturday.
The 26-year-old's baby was delivered at the scene and is currently fighting for its life in hospital.
Posting on Facebook, Ms Fauvrelle's brother, Stephan Alexander Simpson wrote: "Words can’t describe the pain we’re feeling.
"You couldn’t have been a better sister, and I thank you for always being there for me, helping whenever I needed it.
"A beautiful person who’s life has been taken from her.
"I’ll stay strong, you’ll always be in my thoughts, so please keep watching over us.
"I love you more than you can possibly imagine.
"Rest in peace Kelly"
A murder investigation into what a senior detective branded a "horrific incident" has been launched.
Ms Fauvrelle was found with stab injuries and died in Raymead Avenue, in Thornton Heath, Croydon at around 3.30am on Saturday.
A 37-year-old man has been arrested on suspicion of murder and has been released under investigation pending further enquiries, with the force stating officers "retain an open mind to any motive".
A 29-year-old man was also arrested on Saturday on suspicion of murder, and has been bailed until the beginning of August.
Detective Chief Inspector Mick Norman said: "This is a horrific incident in which a young mother has lost her life and her child is critically ill.
"Our sympathies go out to her devastated family.
"They are being supported by specially trained officers following this awful event, and I would ask that they are left alone at this time as they come to terms with the enormity of what has happened.
"A large crime scene is in place, and is likely to be in place for some time.
"At the forefront of our inquiries is understanding what exactly has led to these tragic circumstances, and we are doing everything we can to establish the facts."
Medics fought to save Ms Fauvrelle after an air ambulance, two ambulance crews and two response cars were sent to the scene by the London Ambulance Service.
A post-mortem examination will be held in due course.
A London Ambulance Service spokesman said they were called at 3.26am on Saturday to reports of an incident on Raymead Avenue, Thornton Heath.
"We sent an incident response officer, two ambulance crews, two medics in response cars and an advanced paramedic to the scene. We also dispatched London's Air Ambulance," he said.
"We took one person to hospital as a priority. Sadly, despite the extensive efforts of medics, another person died at the scene."
Reacting to the murder on Twitter, London mayor Sadiq Khan said: "Violence against women is endemic in society and devastating murders in the home, like this one, show the scale of the problem we face.
"My prayers are with this innocent child, and with the mother it has so tragically lost."
Neighbours expressed shock and sadness at the attack, Monica Bejan told ITV News the street was "full of police and ambulances," causing her to panic about what had happened.
Another neighbour, Florentina Solovastiu, said she saw a doctor carrying the baby out of the house and into an ambulance.
Anyone with information should contact police on the dedicated incident room number of 0208 721 4005, or ring 101 quoting CAD 1358/June 29. Alternatively, contact Crimestoppers on 0800 555 111.