A new suspect police want to quiz over Madeleine McCann's disappearance 12 years ago is understood to be a German child sex fiend killer.

Detectives in Portugal are closing in on a foreign paedophile of 'considerable significance' following a tip off from Scotland Yard.

Prolific pervert and convicted triple-murderer Martin Ney, 48, is believed to be one of the two key 'persons of interest' officers are now focusing on and are set to quiz behind bars.

Maddie's parents Kate and Gerry are yet to be informed of any fresh leads.

Martin Ney, 48, is believed to be one of the two key 'persons of interest' officers are now focusing on (left), and a previously issued suspect's photofit (right)

Madeleine McCann disappeared from the Ocean Club resort in Portugal's Praia da Luz as a three-year-old in May 2007

Ney was jailed for life in 2012 for abducting and murdering three young children and abusing many more, The Sun reported.

The killer, known as the 'masked man', was reportedly known to haunt the Algarve and travelled throughout Portugal in the 1990s.

He revealed in chatroom messages, under the username GerdX, he had dressed in camouflage to jump out of bushes, 'in children's playgrounds if a beautiful boy goes past,' The Sun reported.

He also wore masks, balaclavas and replied 'yes' when one girl awoke from a nap and asked if he was her daddy.

Ney was jailed for killing Stefan Jahr, 13, in 1992, Dennis Rostel, eight, in 1995, and Dennis Klein, nine, in 2001.

His known victims are all boys, but experts claim gender is often unimportant for paedophiles.

It was reported last year that Ney confessed a fourth killing to a cellmate, that of 10-year-old French school boy Jonathan Coulom, who was kidnapped and killed from a holiday camp in Saint-Brevin-les-Pins in 2004. This has not resulted in a charge.

He was also investigated over the disappearance of German boy Renee Hasse in Aljezur, Portugal, in 1996, but never charged.

He is known to have finished his teacher training aged 21 before travelling to Ecuador in 1993, Peru in 1995 and Portugal a year later. He was jailed in 2012 after a wide scale police operation.

Former disgraced Portuguese Police chief Goncalo Amaral gave a recent interview to Australian journalist Mark Saunokonko in which he claimed police were on the verge on naming a new Maddie suspect, a German paedophile whom he didn't identify.

Family spokesperson Clarence Mitchell said of potential new kidnapper Ney: 'It might be him and he fits the profile, he is a known predatory paedophile and he's a foreigner.

'He wore camouflage gear, carried knives and jumped out of bushes to pounce on victims.'

Ney is believed to have leapt out at children from behind bushes wearing a mask and dressed all in black (photofit pictured)

He told MailOnline: 'It is quite possible and plausible police are looking at him again but it could be someone else. There is a degree of credibility it is Ney but we cannot speculate.

'Ney has been previously interviewed by detectives over Madeleine's abduction, and denied it. He is in a German jail now.'

Mr Mitchell said that Portuguese Police's fresh bid to close in on Maddie's kidnapper was 'action on a tip off from Scotland Yard.

He explained: 'The Yard has been doing a fair amount of work on this new person of interest and they then ask Portuguese officers to nail it down.

'If activity needs to be done, the local police have to do it even if it's a foreign force's investigation. And if Ney is the person of interest a German force will then have to get involved to interview him on their soil.'

He added: 'Kate and Gerry are not in a position to comment on this, nor would they because it is operational detail and they will not discuss it.

Police are reportedly pursuing two theories and two potential suspects including the German paedophile and another revolving around a suspect in another country

Police investigating the disappearance of Madeleine McCann are focusing on a convicted German paedophile

'It is purely for the police if they choose to comment. The family will wait to hear of any developments and remain grateful to the British police for everything they are doing.'

A close friend of the McCann's said: 'If Ney is the suspect can you imagine how Madeleine's parents will be feeling, knowing that a child killing pervert may be involved in their daughter's kidnap. It is beyond horrendous.'

Kate has previously said there is 'always the worst case scenario' as she told of her need to know if Maddie dead or alive.

She said in an interview to mark the seventh anniversary in May 2014 that not knowing was the worst thing.

She said: 'But there is always the worst case scenario. That's always been a possibility and anyone who thinks that we're blinkered doesn't know us.

'We obviously want Madeleine back number one, but we want an answer whatever.

'I'm not underestimating the blow of hearing bad news that your child has been killed, because obviously we're not going to go 'OK, at least we know.'

'But I've spent hours thinking about that and, each time, I still come up thinking we need to know.'

It is understood the new suspect, who is already in prison, has only been recently identified

Former GP Kate, 51, now a medical worker, told in her 2011 best seller book 'Madeleine' that several witnesses reported seeing 'men behaving suspiciously' around the Ocean Club resort in Portugal's Praia da Luz where Maddie vanished from as a three-year-old in May 2007.

Kate of Rothley, Leicestershire, said: 'The witnesses helped to produce images of these men.'

Of four, two look very similar and have been likened to Ney.

