German prosecutors are investigating whether the prime suspect in the disappearance of Madeleine McCann was involved in a similar case of a five-year-old who went missing in Germany in 2015.

The development comes as newly emerged police reports show that the suspect, a 43-year-old German rapist and child sex offender identified by Portuguese sources on Thursday as Christian Brückner, allegedly fantasised about abducting and sexually abusing minors in a 2013 online chat.

Circumstantial evidence has convinced detectives that Brückner is the strongest suspect yet since the British girl Madeleine disappeared in 2007, aged three. Police in Germany, the UK and Portugal made a major appeal for evidence on Wednesday.