Dutch historians are reopening investigations into who made the anonymous phone call which led the Nazis to the hiding place of Anne Frank and her family on a warm summer evening in 1944.

We don't have a favourite at the moment, but we're going to look carefully at the arguments

David Barnouw Historian

Anne's teenage diary of a Jewish family in hiding in occupied Amsterdam has been translated into dozens of languages and read by millions worldwide.

But to this day, nobody knows for sure who told the Nazis about their presence in the Amsterdam canal house - making a telephone call which ultimately led to the deaths of Anne, her sister and her mother in German concentration camps.

"We decided to look again at the issue because there have been a couple of books published recently which suggest new suspects," historian David Barnouw of the Netherlands Institute for War Documentation (NIWD) told BBC News Online.

"We don't have a favourite at the moment, but we're going to look carefully at the arguments - and maybe we'll pin down the culprit."

Petty thieves and cleaners

For years after the war, Willem Van Maaren - who worked in a warehouse near the Franks' hiding place - was the chief suspect, but that theory was seen as unconvincing by many historians.

A bookcase hid the door to the Franks' hiding place

He died in 1971 professing his innocence, but only recently have new suspects emerged to take his place.

In a book published this week, British historian Carol Anne Lee points the finger at two men - Anton Ahlers, a petty thief and former business associate of Anne's father, and Dutch policeman Maarten Kuiper.

Ms Lee argues that Mr Ahlers knew where the Franks were hiding, and gave Mr Kuiper the information, who then made the call.

"They were friends. Ahlers had so much information on Otto Frank. Maarten Kuiper was one of the major betrayers of Jews in hiding during that time," she says.

Meanwhile a book by Austrian historian Melissa Mueller names cleaning woman Lena Hartog as the culprit.

Mrs Hartog cleaned a shop in the building where the Franks were hiding. Ms Mueller says she knew they were there, and feared that ultimately they would be found, and everyone in the building would be punished.

A team of historians from the NIWD will go through the documents unearthed by the historians and seek to evaluate their arguments.

"We may even find a few new suspects in the process," said Mr Barnouw, adding that the institute's findings would be published before the end of the year.