Detectives investigating the abduction of Madeleine Mccann flew to Portugal to interview two former friends of chief suspect Christian Brueckner.
Elke Piro, 69, and husband Bernhard, 72, put Brueckner up in their home just a few months before Madeleine vanished from an Algarve holiday apartment in 2007.
The couple were interviewed last week as the suspect was freed from a seven-year prison sentence for the rape of an elderly woman at her home in Praia da Luz in 2005.
Operation Grange officers spoke to the couple for several hours about their acquaintance with fellow German national Brueckner, 49, The Sun reports.
Mrs Piro said: “The British police interviewed us a few days ago but I’m sad because I wasn’t able to tell them anything I haven’t said before.
“It’s frustrating because I got to know Christian over many years and believe he did something bad to Maddie.
“My hope now is the police can find a way to bring him to trial in the UK. That would be wonderful. I will be happy to co-operate and testify in court if needed.”
Brueckner remains a suspect in the Met's investigation into Madeleine’s disappearance. The force revealed he rejected a request to be interviewed last week.
Mrs Piro shared her view that Brueckner may have come across three-year-old Madeleine as she slept while burgling the McCann's holiday apartment looking for cash.
She thought may have Brueckner taken the girl and panicked, before doing "something terrible".
Mrs Piro described her horror at learning of Brueckner's sexual offending history and wished he'd "never come into our lives".
The interview emerged as Met Police chief Sir Mark Rowley suggested Brueckner could be extradited if new evidence came out in the case.
The couple were questioned at a police station in Faro, and said they met Brueckner in the Algarve in 1995, and were acquainted with him up until 2018. They have previously spoken to German and Portuguese detectives.
Mr Piro described Brueckner as a "classic sociopath" and said he regretted allowing him to stay in a camper van outside their home in Barrocal, 45 minutes' drive from Praia de Luz.
His wife described the suspect as someone who veered from being "kind and gentle" to "crazy" and "raging about sex" when drunk, calling him a "terrible alcoholic".
When in a good mood, Brueckner could be "charming" and she used to iron his shirts.
Mrs Piro said she never felt threatened by Brueckner, but he there was "something strange" about him that made her uncomfortable and she didn't allow him to stay overnight.
She said she became used to his outbursts, including a misogynistic rant about women which he directed to her 15-year-old son.
She added they knew Brueckner was "a liar and a crook" but her husband tolerated him because he pitied him and wanted to help him.
She said they "had no idea what he had done at the time".
Brueckner left the high-security prison in Sehnde near Hanover on Wednesday morning, German police said and will have to wear an electronic ankle tag for the next five years.
German media also reported that he will have to give up his passport, although his lawyers are expected to appeal against the conditions.
Prosecutors still believe Brueckner was responsible for the girl’s disappearance, and Mr Wolters said Brueckner’s release from prison has “no direct impact” on the probe.
“The release of Christian B has no direct impact on the McCann case,” Mr Wolters said.
Brueckner has not been charged in the case, in which he is under investigation on suspicion of murder.
He has previously denied any involvement in her disappearance.
Authorities also say he is still dangerous, following a recent psychiatric report that concluded he is likely to commit further crimes after he failed to undergo any therapy while in custody, according to reports.
A court hearing is also listed for October 27 in Oldenburg in north-west Germany, to deal with a case in which he is accused of insulting a prison employee.
