Investigators spent several hours quizzing a couple who housed the sex offender just three months before Madeleine vanished from her family's holiday apartment in Portugal, in May 2007.

Christian Brueckner , 48, had been serving a seven-year term at Sehnde prison for an unrelated offence before being released at 9:15am local time this morning.

Met chief Mark Rowley says many questions remain and detectives are liaising with German and Portuguese police