Police say they will continue to search day and night for the missing baby of an aristocrat's daughter, Constance Marten and her boyfriend Mark Gordon, and say there is a chance the child "has come to serious harm".
Marten and Gordon remain in custody after being put under arrest on suspicion of gross negligence manslaughter, and detectives have since sought a further 36 hours to continue questioning them.
In an update on the inquiry, officers said they were continuing to search an area of 90 square miles. Teams supported by helicopters and sniffer dogs will be continuing the operation throughout the days and nights ahead.
They are also continuing to appeal to the public to come forward with any reports of suspicious behaviour or items they might come across.
Police are carrying out tests on the baby's placenta that was found in the couple's abandoned car on the M61 in Bolton, Greater Manchester, on January 5.
A woodland area remains cordoned off by officers as they conduct sweeps of Moulsecoomb Wild Park and they have since searched every shed at Roedale Valley Allotments before extending their efforts into the park towards Hollingbury Golf Course.
In newly-released CCTV footage from just hours before their arrest, the couple is seen arguing in the street, with Gordon appearing injured and walking with a large stick.
Detective Superintendent Lewis Basford said officers are looking into the footage, adding that there was sufficient intelligence to suggest the pair had spent most of their time in outdoor open spaces while avoiding the police.
A neighbour who spotted the pair said she first saw them walking without any bags at 8.40pm, returning at 9.25pm with two bags of food from a shop.
She told The Sun: "He was shouting. It was yelling. He was very angry. He had this big stick which was random.
"He was shouting at her. He was animated. They were having an argument.
"Looking back it’s really scary. I’m terrified for that poor baby. There was no sign of a baby when they came by."
Ch Supt James Collis, of Sussex Police, says house-to-house enquiries will commence as he told reporters in Brighton this afternoon: "Hundreds of officers from Sussex Police and the Metropolitan Police have been searching tirelessly overnight and that search is continuing over an extensive area today.
"I would once again like to thank the local community for their patience and understanding while we carry out this investigation and search.
"The increased police presence is likely to be in place for some time still, which will include additional search parties, extra patrols and house-to-house enquiries."
The lengthy police search for Marten, 35, and Gordon, 48, began on January 5 when their car was found on fire abandoned next to the M61 in Bolton.
Inquiries revealed Marten had given birth recently - possibly one or two days before the incident - and had not been assessed by medical professionals.
They used taxis to first travel to Liverpool, then Harwich in Essex, and on to east London, before arriving in Sussex on January 8.
The couple avoided detection by only making payments in cash, hiding their faces on CCTV and often moving around at night or in the early hours of the morning.
Their baby was born in early January and has had no medical attention since then, with its parents sleeping rough in freezing temperatures much of the time.
It is unknown if the infant was full-term or has any health issues.
Anyone who may be able to assist in the search for the baby is urged to contact 999.
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