Police investigating the disappearance of Madeleine McCann have gone to Bulgaria in search of the 'woman in purple' - a figure who is keeping the operation alive, reports the Daily Mail.
Waitress Luisa Todorov, 58, is believed to be the mystery woman seen by two witnesses standing outside apartment 5a of the Ocean Club from where Madeleine was taken 10 years ago.
One witness saw her standing by a lamp post just outside the apartment at 8pm on May 3, 2007 and another saw her about half an hour later nearby.
Mrs Todorov's husband Stefan, 50, was working at the tapas bar at the Ocean Club where the McCanns and their seven holiday friends were dining when Madeleine was abducted.
Mr Todorov had been in Portugal since November 2002 and also worked as a car painter.
The couple, who both worked at the restaurant 500 metres away from the apartment block, gave statements to police five days after Madeleine's disappearance.
They both denied having any knowledge of the case and have not been spoken to again for over a decade.
Heriberto Janosch González, who has been investigating the case for 10 years, is convinced Mrs Todorov is the mystery 'woman in purple'.
He said: "I have been combing through all the police files trying to identify who the woman in purple could be.
'It has been widely reported that Yard officers are in Bulgaria.
"Examining all the known statements it seems highly likely the police are seeking the Todorovs. They are the only known people with a clear link to Bulgaria."
According to their witness statements Mrs Todorov finished her shifts at 6pm while her husband started at 8pm until midnight having worked as a car painter during the day.
Jenny Murat, 79, whose son Robert was the first official suspect, but was formally cleared of suspicion in 2008, has told how she noticed a woman outside the apartment in Praia da Luz, which Maddie vanished from in 2007.
Talking of when she spotted the woman in purple, Mrs Murat said: "I saw the woman standing on the corner of the street.
"She caught my eye because she was dressed in purple-plum clothes. It struck me as strange.
"It's so usual for anyone, particularly a woman, to be standing alone on the street in our resort, just watching a building.
"The next morning, we heard that a little girl had gone missing, and I later told police about the woman I'd seen right outside. I didn't recognise her and don't have a clue who she is, but she seems a bit suspicious."
In the past few months, the Grange team - now down to four detectives from a peak of 31 - has been criss-crossing Europe trying to locate the woman.
Their budget had been due to run out in September, but officers are understood to have used the "woman in purple" line of investigation to persuade the Home Office - which is financing the inquiry from central government funds - to grant a six-month extension.
The £154,000 agreed will allow inquiries to continue until March, taking the total spent on Operation Grange near to £12 million.
During the past six years, a string of theories and suspects have come and gone.
Variously, the spotlight has fallen on a group of British contract cleaners working in the resort, a smelly, pot-bellied man, a burglary gang posing as charity collectors, child-traffickers and gypsies.
Operation Grange has been one of the longest, most high-profile and costly police investigations in history.
Launched in May 2011, officers have sifted (and translated) 40,000 documents produced by Portuguese police who conducted the initial investigation, and by the eight teams of private detectives who have worked on the case.
Some 600 "persons of interest" have been examined and "sightings" of Madeleine - in Brazil, India, Morocco and Paraguay, on a German plane and in a New Zealand supermarket - assessed.
The Portuguese investigation of Madeleine's disappearance was criticised by the British authorities as being not fit for purpose.
Scotland Yard began an investigative review into the disappearance in 2011, on the orders of then-Prime Minister David Cameron.
However it is understood Met detectives have been relying on Portuguese transcripts of key interviews with British witnesses, rather than conducting their own.
Operation Grange has conducted no formal witness interviews with Gerry or Kate McCann or the seven friends they dined with on the night Madeleine disappeared.