What did the stepmother do?

In truth, Zahra lost her leg to bone cancer, but such was the character of the child, described by those who know her as plucky and possessing ''an absolutely great personality''.

But police in the small industrial town of Hickory, in North Carolina, say Zahra, who was born and lived in Australia until last year, is almost certainly dead.

Suspicion has fallen upon her 42-year-old stepmother, Elisa Baker, who describes herself on her MySpace page as a ''Gothic'' and who is being detained after she admitted to writing a ransom note that was discovered in the Bakers' car. Police plan to charge her with obstructing justice.

But the case is full of mystery. Police say they cannot find anyone - other than her immediate family - who has seen Zahra in at least a month, although Ms Baker and her husband, Adam, didn't report her missing until Saturday.

And as her disappearance gained publicity, relatives of Ms Baker have said Zahra appeared to have been mistreated.

On Tuesday, Hickory police switched the focus of their investigation from a missing person or abducted child case to a homicide investigation.

Last night, officers and FBI agents were searching through piles of woodchips at the Hickory plant of a tree trimming company that employed Mr Baker.

Zahra was born in Wagga Wagga and moved to North Carolina with her father last year after he met Ms Baker on the internet. The couple married in July.

Zahra's mother lives in Australia but is believed not to have had any contact with her daughter since Zahra was a baby.