Portuguese police say says they had "nothing concrete" to implicate missing toddler Madeleine McCann's parents in her disappearance.
The comments, from a senior officer, seem to be a step back from charging the McCanns with her disappearence.
Detectives may be depending on Kate and Gerry McCann making a confession in order to prove their suspicions, a Portuguese newspaper reports.
The couple were declared formal suspects in the case exactly a week ago, and are now back in Britain waiting to learn whether they will be charged.
Maddie’s death not confirmed
A "high-ranking" officer in the Policia Judiciaria (PJ) – Portugal's criminal investigation department – says the evidence is not even strong enough to prove whether Madeleine is dead.
It is now 134 days since the young girl vanished from her bed in her family's holiday apartment in the Algarve resort of Praia da Luz.
The unnamed PJ officer told the 24 Horas newspaper: "We have nothing concrete.
"There are a lot of indications, but without more elements it's impossible to determine what happened in those four vital hours in the case (between 6pm and 10pm on the night Madeleine vanished).
‘Can’t prove anything’
"Even if the blood and traces gathered in the car or in the apartment were confirmed to correspond 100 per cent to the little girl's DNA, that wouldn't prove anything.
"Those elements could only confirm – and that doesn't even happen – that the little girl was in the apartment (which is obvious) and in the car.
"In either of the cases nothing would prove homicide, just that the body of the little girl had been transferred in the vehicle.
"We don't know if Madeleine is dead, and if she is, how it all happened.
"Was she strangled? Could she have been beaten? They are questions only the parents could clarify in an eventual confession."
This appears to contradict a report that the Forensic Science Service in Birmingham is examining bloodstains from the apartment next to the McCanns'.
Police believe this sample could hold the key to where Madeleine's body could have been stored after she vanished, the Evening Standard says.
The McCanns left their home in Rothley, Leicestershire, just before 10am today and spent the day in meetings with their London-based lawyers, Kingsley Napley.
A friend says Madeleine's parents were under intense pressure but were "not cracking up".
On Tuesday the PJ formally passed their 4,000-page dossier of evidence against the McCanns to Algarve-based public prosecutor Jose Cunha de Magalhaes e Meneses.
He immediately ordered that the 10 lever-arch files should go before a criminal instructional judge, understood to be Pedro Daniel dos Anjos Frias.
The judge now has until next Thursday to consider a number of requests made by the prosecutor, among them that he approve the seizure of Kate McCann's personal diary, sources say.
Portuguese newspapers claimed today that police are investigating whether the McCanns had any "accomplices" in allegedly disposing of Madeleine's body and concocting a false story.
Detectives have admitted that the young girl's body may "no longer exist", according to the Diario de Noticias.