Police searching for the parents of three newborn babies, all abandoned in east London minutes after their birth, say they are now focusing on about 400 nearby houses.
Baby Elsa was left in a Boots carrier bag near a footpath in Newham on 18 January 2024, before being discovered by a dog walker.
Subsequent DNA tests established she was the sibling of two other babies, a boy and a girl, each found in very similar circumstances in 2017 and 2019.
Despite police appeals, the parents of the three babies have still not been identified.
Over the last five weeks, detectives searching for the parents have given BBC News access to part of their operation.
They allowed us to follow officers going door-to-door asking residents to provide DNA samples to see if they are connected to the babies.
They are also contacting people they have found using the national DNA database who may share familial DNA with the children's mother.
Officers who recently met Elsa told the BBC the toddler is a bright girl who is curious and engaging.
It was on 17 September 2017, when the first baby, Harry, was found, over a mile to the west of the spot Elsa was left – just north of the Greenway, a four-mile long footpath and cycleway in Newham. He'd been left in a bush in Plaistow Park, wrapped in a towel.
Sixteen months later, his sister Roman was discovered on a bench by a dog walker in the small children's play park, in Roman Road.
She was found on a freezing evening, at about 22:15. Roman was wrapped in a towel, inside a Sainsbury's shopping bag.
The babies' names were given to them by emergency staff who helped them – they have all since been changed.
DNA tests revealed that Harry and Roman were full siblings, however, that information wasn't initially made public.
It was only when Elsa was found five years later, and the case came before the family court, that we were able to report all three babies had the same parents.
Det Insp Jamie Humm, who became the case's senior investigating officer after Elsa was found, says "it wasn't a huge shock" when DNA confirmed she was the sister of the other two babies.
Elsa had been abandoned just a few minutes' walk from where Roman was found.
For the first 12 months after taking on the investigation, Det Insp Humm assumed the babies' mother was able to contact police, but had been reluctant to do so.
His team scoured the area, knocking on doors, talking to local people, but no-one had seen or heard anything.
In January this year, the charity Crimestoppers offered a £20,000 reward for information, which also proved fruitless.
