British police have arrested an aristocrat and her partner after the pair went missing with their newborn baby in early January, but the search for the infant continues.

In an update Tuesday, London’s Metropolitan Police said in a statement that Constance Marten, 35, and Mark Gordon, 48, had been “initially arrested on suspicion of child neglect,” but were later “further arrested on suspicion of gross negligence manslaughter.”

Police said that the couple’s baby, whom they believe was born just before the pair disappeared without receiving medical attention, is still missing.

“Throughout this investigation our key priority has been finding the baby, and we remain committed to that,” Detective Superintendent Lewis Basford said in the statement.

Police helicopters, sniffer dogs, thermal imaging cameras and drones are all being used to assist the over 200 officers on the ground in their search for the baby, the police statement added.

Prior to their arrest, the couple were spotted in Brighton, southern England, on Monday night, police had said earlier on Tuesday.

Basford said a member of the public there “quickly called police” on Monday night after spotting the couple, enabling police to get “on the scene within minutes to make the arrest.”

He also appealed to residents of the area to report any potential sightings or information about where the couple may have slept.

The search for the couple and newborn began in early January, with police releasing several appeals and offering a £10,000 ($12,090) reward for information that would lead to their discovery.

Marten is the daughter of aristocrat Napier Marten, a film and music producer. In an audio appeal to his daughter, published by UK news outlet The Independent last month, Napier Marten said Constance was “much, much loved, whatever the circumstances,” adding that the family was “deeply concerned” for her and her child’s welfare.

“Darling Constance, even though we remain estranged at the moment, I standby, as I have always done and as the family has always done, to do whatever is necessary for your safe return to us.

“I beseech you to find a way to turn yourself and your wee (little) one into the police as soon as possible so you and he or she can be protected. Only then can a process of healing and recovery begin, however long it may take, however difficult it may be,” he added.

In a renewed appeal for information last week, Basford said more than 630 hours of security camera footage had been reviewed and police had received more than 350 calls from members of the public.

He explained at the time that they were “not doing this and putting so many resources and efforts into finding the family just to be awkward or to interfere,” but explained the police “have a genuine concern for the health and wellbeing of the baby, and Constance and Mark, and it our duty to ensure that they are okay.”

Timeline

On January 5, police inquiries identified Marten and Gordon as the occupants of a car that had caught fire on a highway in the northwestern town of Bolton, England.

The pair were not at the scene and most of their belongings were destroyed in the fire, according to police, who launched a missing persons investigation.

Several confirmed sightings of the couple by members of the public were reported in the days following their disappearance.

The pair and their baby had left the highway safely, and police used sightings and security camera footage to map their movements through various UK cities and towns.

On January 7, the pair were seen in London with their faces covered leaving a taxi with an orange carrier bag and a pram.

Using cash, they paid for various items, including a two-man tent, two sleeping bags and two pillows, which made detectives fear they had been camping or sleeping rough, at a time of cold temperatures.

The couple dumped the buggy and other items later that day before continuing to travel. (CNN)

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