Yesterday, as the first picture of the 6ft 2in ex-waiter emerged, detectives were investigating the possibility that he kidnapped Madeleine after being disturbed as he broke into her family’s apartment.
Menteiro, known as Toni, died aged 40 in a tractor accident four years ago.
But phone records have placed him near the flats at the time she vanished. It is believed he may have been raiding guests’ rooms to feed his heroin habit.
His picture looks nothing like two e-fit images issued by Scotland Yard – but police stress they are still exploring every line of inquiry.
Nelson Rodrigues, 32, a barman and waiter at the Ocean Club for two years, worked alongside Monteiro in 2006.
He said yesterday: “On the surface he was a nice guy but there was something not right with him.
“He would turn up to work with bleary eyes, sometimes he didn’t seem like he was all there.
“And things were going missing about that time – laptops, jewellery, mobile phones, anything that was lying around.”
Mr Rodrigues said police were called after Monteiro was accused of stealing tips. He was searched, but nothing was found and he protested his innocence.
Later an officer for Portugal’s national guard took the staff to one side and warned them about Monteiro.
Mr Rodrigues recalled: “The officer told us, ‘We know him, you can’t trust that man’. They said he’d been in trouble in the past for drug offences.
“That’s the last time he worked at the Ocean Club. I never saw him again.”
Monteiro, originally from Cape Verde islands off West Africa, was convicted of theft in 1996 but escaped deportation after a presidential pardon.
He was living in Lagos, a 15-minute drive from Praia da Luz, when Madeleine disappeared.
British expat, George Burke, from Liverpool, reported a possible sighting in Lagos.
He said he saw a girl “remarkably like Madeleine” being dragged along a road to Lagos marina at 6am the day after she went missing.
But Monteiro’s relatives claim police are just looking for a “scapegoat”.
His sister Paula said: “It’s ridiculous – the e-fit they released is a white man and my brother was black. He loved kids. He had a son and daughter and would never have harmed a young girl.”
Last week it was revealed Madeleine’s parents, Kate and Gerry, are to apply under Portuguese law to become private “prosecutors”.
It may help them influence the course of the investigation and any future prosecution.