The forensic evidence that Portuguese investigators are using to label Kate and Gerry McCann suspects in their daughter's death is inconclusive, according to a report published Friday.

The McCann's daughter, Madeleine, disappeared while the McCanns were on vacation in Portugal in May. The investigation first focused on an outside perpetrator but last week zeroed in on the parents.

"We have nothing concrete," said a high-ranking official in Portugal's Polícia Judiciária, according to a London Times report based on Portugal's 24 Horas newspaper.

Click here to read the full London Times story.

"There are a lot of indications but without more elements it is impossible to determine what happened in the four vital hours in the case," the official said.

The evidence does not even prove Madeleine is dead, the official said.

"We don't know if Maddie is dead and if she is how it has happened. Was she strangled? Could she have been beaten? They are questions only. The parents could clarify in an eventual confession," the official said.

Detectives have been unable to create an accurate timeline of events after 6 p.m. on May 3 when Madeleine was taken by her parents to their holiday apartment on the Algarve to prepare her for bed, the London paper reported. Kate McCann said she discovered Madeleine's bed empty when she made a check on the apartment at 10 p.m.

Portuguese police want to reinterview some of the British friends who had travelled with the McCanns to Portugal and were with them at the Ocean Club when Madeleine disappeared, the Times of London reported. A team of Portuguese detectives are believed to have already travelled to England.

Reports have suggested that traces of hair and bodily fluids discovered in a Renault Scenic rented by the couple 25 days after Madeleine's disappearance prove that her corpse had been in the boot.

However, the officer quoted by 24 Horas believed otherwise.

"Even if the blood and the traces gathered in the car and the apartment were confirmed to correspond 100 per cent with the little girl's DNA that would prove nothing," the officer is quoted as saying.