Police have given different reasons for arresting James Ricketson, 68, ranging from espionage, living illegally in the country and flying a drone without permission.
Officers at the Phnom Penh Municipal Police headquarters refused to clarify the situation yesterday.
"We are working on the case," a senior officer at the police immigration told the ABC.
He declined to elaborate or fully identify himself.
However, other media reports suggest his name is Colonel Chea Chettra and the ABC understands he is overseeing Mr Ricketson's case.
Under Cambodian law, a suspect can only legally be held for 72 hours before being charged.
Mr Ricketson remained in detention in Phnom Penh's northern Toul Kouk district last night, as the legal detention period expired.
Confusion over reasons for arrest
It is not clear why Cambodian police arrested Mr Ricketson.
Separate articles in newspapers aligned with Cambodia's ruling party quoted immigration official Lou Rabo and deputy chief of the Phnom Penh municipal major crimes unit, Tey Visal, saying Mr Ricketson was arrested for flying a drone at a political rally on Friday.
However, the same immigration official, Lou Rabo, told the English-language newspaper The Cambodia Daily a different story.
"Photographs posted online to government-aligned Fresh News appear to show Mr Ricketson operating a drone over a crowd of CNRP campaigners, but Mr Rabo denied that the arrest was prompted by this," reported The Cambodia Daily.
The newspaper wrote that police had asked Mr Ricketson for his passport and "he didn't have it".
"This means he is living in Cambodia illegally," Mr Rabo said, according to The Cambodia Daily.
Further confusing the situation, the Khmer Times quoted police saying the Australian had been released.
"After his arrest and questioning he was released by the court prosecutor because Cambodia does not yet have a law to punish those who take pictures in prohibited areas," said Tey Visal, from the Phnom Penh municipal major crimes unit.
The report of his release was incorrect.
Ricketson involved in controversy and charity
Mr Ricketson is well known around Cambodia's capital for helping poor families.
His most recent Facebook posts were portraits of scavengers at Phnom Penh's rubbish dump, which he visited to donate food.
But Mr Ricketson is also a controversial figure, engaging in long-running feuds with organisations and individuals, played out on his blog and in the courts.
In 2014, he was fined $2,000 and given a two-year suspended sentence for defamation, over a dispute with a Brisbane church working in Cambodia.
In December, Mr Ricketson was ordered to pay $4,900 in fines and compensation for defaming anti-paedophile organisation Action Pour Les Enfants.
Recently his blog has focused on a long-running dispute with Screen Australia, partly over their gender equity quotas for funding.
A blog entry from 2013 said he was working on a documentary about Sam Rainsy, a Cambodian opposition leader who fled the country on what are widely considered trumped up charges.
The Australian embassy is aware of the case.
"The Department of Foreign Affairs and Trade is providing consular assistance, in accordance with the Consular Services Charter, to an Australian man detained in Cambodia," a spokeswoman from Australia's Department of Foreign Affairs and Trade said.