The new Madeleine McCann suspect has been on the police radar for more than 20 years.
A British woman who dated Christian Brueckner when she worked as a barmaid in the Algarve has spoken about, in the course of their relationship, he changed from a "charming" man to a possessive, violent cheater and stalker.
Speaking to the Mirror in the UK, Brueckner's ex-girlfriend revealed he broke into her flat through a window and lay there waiting for her under her bed, hours after he brutally attacked her in a jealous rage, when he'd caught her innocently hugging another man.
She returned home with a "horrible feeling" someone was inside. Then she found him under her bed.
The 45-year-old woman believes he was there waiting to attack her if she had brought another man with her back to her flat.
Instead, she says Brueckner looking at her, said "goodbye" and fled the flat.
From then on, she says he started a stalking campaign against her and she became afraid to walk home alone.
She also says he left her covered in her own blood after repeatedly slamming her head against the wall in he ladies' toilet of the bar where she worked in the Algarve.
Twice she called Portuguese police to protect herself from Brueckner. However, he was never charged.
The break-in is reminiscent of what Gerry McCann says happened to her daughter in Praia da Luz.
He believed the abductor was behind a door when he went to check on his daughter. Investigators say the abductor may have entered the apartment through a window.
The ex-girlfriend, who still fears Brueckner and didn't want to reveal her identity, told the Mirror the German paedophile seduced her while they worked together in an Algarve restaurant.
He branded her a "lazy Brit" when he ordered her to clean his house and she refused.
The woman says she believes he could be responsible for Madeleine McCann's disappearance.
"Until now I've refused to believe someone I was involved with could commit such a horrible and disgusting thing like hurting a child," she told the Mirror.
"But I'm not sure anymore. I'm starting to wonder if he did do it. And if he did, he needs to be really punished for it.
"It's chilling to think my ex is suspected of abducting Madeleine McCann. I can't cope with it."
She says that her ex could be "very, very charming, very funny and very smooth in the way he talked".
"He always dressed nicely, holding the door open for women, that kind of thing.
"I was alone here in Portugal, no family around and a bit lonely and I was getting all this attention from this guy," she added.
"We got together romantically and at first it was great. The relationship was very nice."
She says he wasn't "sleazy" in the beginning but didn't take long to change.
"He drove the nice car - the black Jaguar - and was very gentlemanly and spoke properly.
"Our sex life was normal. He wasn't into anything weird with me," she added.
"At first he seemed very easy-going, very relaxed, but gradually after summer things changed.
"During the summer it was good, but during the winter it started to get not so good."
READ MORE:
• Madeleine McCann 'murder' suspect told barmaid 'the child is dead and that's a good thing'
• Maddie McCann murder suspect's chilling message to girlfriend day before 3yo disappeared
• Witness 'saw Madeleine McCann getting into VW van weeks after disappearance'
• Ex-detective says Madeleine McCann case 'unsolvable' because crucial CCTV camera was turned off
They started arguing about small things and he became very jealous of any male friends she had.
"He also began going back and forwards to Germany over that time. He'd stay one week in Germany, then back to Portugal," she said.
"I remember feeling suspicious, like something strange was going on, so I looked at his phone.
"I found messages in German from someone called 'B' saying 'Ich liebe dich' - I love you.
"It was a German number, and obviously he had been going back and forth to Germany, so I put two and two together.
"I confronted him about those and he went crazy, completely crazy. We had a huge fight."
The pair broke up mid-2005 when she found women's underwear in a bag he owned.
"I confronted him about it at his place and again he went totally crazy.
"He drove me back to Lagos. I got out of his car and that was it as far as I was concerned."
He began stalking her at the restaurant she worked and she had to call the police.
"One day I was carrying a big tray of drinks and because I wouldn't talk to him he knocked them out of my hand and they went everywhere," she recalled.
"The police were called and he was banned from coming inside.
"So he would wait outside and follow me. Sometimes it would be begging me to go back with him.
"But other times it would be him threatening me or saying I'm going to find out where your parents are and do something to them.
"People had to walk me home each night. There was someone each night. Eventually it stopped but it went on for a long while."
The ex-girlfriend says she received a visit from Portuguese police last year, asking her questions about a rape Brueckner carried out on a pensioner in Praia da Luz, not long after they split up.
She says they never mentioned the Madeleine McCann investigation.
"The Portuguese police have spoken to me three times in the past year, but never once did they say it was about Madeleine," she said.
"They said it was about him, they were investigating him because they had found out he had raped an old lady in Luz in 2005.
"They wanted to know all about him. But I had no idea it was to do with Madeleine also."
The first time she found the link between her ex and the McCann investigation was when the news made global headlines last week.
"I was shocked and horrified. Really, really shocked. I couldn't believe I had been with someone who could be capable of that," she said.
"To imagine I've been with someone who is capable of hurting someone like that is sickening."