Evidence provided by Irish couple could help solve the case of Madeleine McCann.

The Irish Independent reports that a two-year review of the case documents by Scotland Yard has been upgraded to a full investigation into the British child's unexplained disappearance on May 3, 2007.

British Prime Minister David Cameron ordered the review, which was nicknamed 'Operation Grange' and was funded by the country's Home Office.

It has identified 38 "people of interest" from a number of European countries, including 12 from the UK.

Martin Smith and his wife Mary, from Maple Drive, Drogheda, Co Louth, provided evidence at the time of the three-year-old disappearance that was considered credible by the review officers.

The couple told investigators that after leaving Kelly's Bar in the resort at around 10 pm, they saw a man carrying a young child through the streets of Praia da Luz in Portugal on the night Madeleine went missing. They said the child's head was lying against the man's left shoulder and her arms were hanging down alongside her body.

Madeleine disappearance from her family's apartment on the Algarve was reported by her parents Gerry and Kate McCann.

The Smiths returned home after the incident, but later traveled back to Portugal to give police a statement about their encounter after seeing the media reports.