A 43-year-old German man, named officially only as “Christian B”, has been identified as a prime suspect in the disappearance of Madeleine McCann.

A spokesperson for the Braunschweig public prosecutor’s office said in a press conference on Thursday that the suspect is being investigated “on suspicion of murder”, adding: “We are assuming that the girl is dead.”

“With the suspect, we are talking about a sexual predator who has already been convicted of crimes against little girls and he’s already serving a long sentence.”

Christian B is known to have lived on the Algarve coast at the time Madeleine vanished on May 3, 2007, while on holiday with her parents, Kate and Gerry McCann, and her twin siblings Sean and Amelie.

A half-hour phone call was made to his Portuguese mobile phone in Praia da Luz around an hour before Madeleine is believed to have gone missing.

The suspect is reportedly serving a seven-year prison sentence for the rape of a 72-year-old American woman in Portugal in 2005.

Reports say he had lived at a rented farmhouse around a mile from the resort, and was staying in a distinctive VW campervan at the time, living in a “transient” manner.

German police have released images of the farmhouse in an appeal for witnesses.

Grassy scrubland near the property on the outskirts of the town was extensively searched by British and Portuguese police seven years later in 2014, but no evidence was found.

Portuguese police would not answer questions about whether Christian B was ever spoken to as part of their initial investigation.

Portuguese detectives were widely criticised for their handling of the case, missing chances to secure potentially key forensic evidence in the apartment room from where Madeleine was taken.

Christian Hoppe, from Germany’s federal criminal police office, said they have not ruled out a sexual motive for the alleged crime against Madeleine.

He said the suspect may have broken into an apartment in the Ocean Club complex, where Madeleine was sleeping, before spontaneously kidnapping her.

The suspect has been linked to an early 1980s VW T3 Westfalia camper van – with a white upper body and yellow skirting, registered in Portugal – which was pictured in the Algarve in 2007.

Scotland Yard said he was driving the vehicle in the Praia da Luz area in the days before Madeleine’s disappearance and is believed to have been living in the van for days or weeks before and after May 3.

The Met Police have received hundreds of contacts from the public after launching a new appeal for information on the disappearance of Madeleine McCann.

More than 270 calls and emails had been received by 4pm on Thursday, according to Detective Chief Inspector Mark Cranwell, who is leading the Met’s Operation Grange investigation into the case.

Operation Grange still considers the case a missing person inquiry because there is no “definitive evidence whether Madeleine is alive or dead”.