LONDON (AP) — British police said they found the remains of a 2-month old baby Wednesday after officers arrested the infant’s mother and her boyfriend, who vanished after the child was born in early January.

Constance Marten, 35, and her boyfriend Mark Gordon, 48, a convicted sex offender, had crisscrossed England to avoid authorities, police said. Investigators suspect the pair used large amounts of cash to live off the grid, traveling around the country by taxi, covering their faces when near closed circuit cameras and moving frequently, often after dark.

They were detained Monday in Brighton, southern England, after a tip came from a member of the public. The baby was not with them.

The couple were initially arrested on suspicion of child neglect, and the grounds were upgraded Tuesday to suspicion of gross negligence manslaughter.

Police had expressed concern that serious harm had come to the baby. Dozens of police officers, assisted with a helicopter and drones, searched for the child in woodland and open areas near where Marten and Gordon were detained.

Detective Superintendent James Collis said Wednesday’s news would be “heartbreaking” for the local community.

Police launched a national search for Marten and Gordon after a car in which they were traveling was found in flames on a roadside on Jan. 5.

Police think Marten gave birth in or near the car a day or two earlier. In the weeks before she and Gordon surfaced, officers said they were concerned for the family’s welfare because neither Marten nor the baby had received medical care.

Marten, who is from a wealthy, aristocratic British family, was reportedly a drama student when she met Gordon. He served 20 years in prison in the United States after being convicted in Florida of kidnapping and sexual battery, according to U.S. law enforcement records. He was deported from the U.S. after his release.

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