But the case may never make it to court because the chief prosecutor has already said he believed the “mud volcano” was a natural disaster, and not caused by a gas exploration well.

Almost a year ago, on May 29, 2006, mud began flowing from a series of vents in the earth during deep drilling at the nearby Banjar Panji-1 gas wildcat.

The flow has not stopped. Even now, about 160,000 cubic metres of mud are spilling forth each day.

Nine villages have since been smothered by sludge, including thousands of houses, factories, mosques and paddy fields, displacing 15,000 people and forcing dozens of businesses to close.

Then in November, 13 people were killed when land subsidence caused by the mud made a gas pipeline crack and explode.

The construction of 23km of earth dykes has failed contain the mud, 20 metres deep in parts, and channel it into the nearby Porong River then on to the sea. Experts now fear mud sediment could eventually choke the river mouth and trigger flooding in Indonesia's second largest city, Surabaya, during future rain seasons.

In January, British experts said the mud volcano could flow for another 30 years.

They also said it most likely began when the improperly cased gas exploration well punched through a layer of rock 2800m below the surface, hitting a huge mud bubble, pressurised by gas underneath.

Surabaya Institute of Technology Disaster Research Centre head Amien Widodo, a geologist, agreed.

"Because they don't use a casing, the mud went wild," he told the Sydney Morning Herald.

The police have reached the same conclusion. According to an AAP report, police say they have questioned 59 witnesses as well as 16 experts in geology, the environment, water management, land degradation and meteorology.

But the prosecutors’ office has on two occasions returned police reports seeking further information.

“According to the investigators, we have sufficient evidence for a trial, but the dossier is still incomplete based on the advice of the prosecutors,” an East Java police investigator told AAP.

East Java provincial prosecutor Mulyono said he personally believed the disaster was a natural phenomenon.

“We will process it [the case] but I don’t know whether it will reach the court.”

The well’s operator, Lapindo Brantas, is owned by the family of Indonesia’s Social Welfare Minister Aburizal Bakrie, one of the country’s leading businessmen and a leading player in the Golkar party, which was the former ruling party in the Suharto era and is still a powerful force in Indonesian politics.

Australian petroleum company Santos owns an 18% stake in the venture, but there is no suggestion the company was at fault and it is not under police investigation.

The other joint venture partner PT Medco Energi sold its entire 32% stake in the drilling concession for $US100 ($A125).

Last November, Medco filed an arbitration claim to seek exemption from paying for the damages, alleging the incident was due to “gross negligence” on the part of Lapindo.

Bakrie has refused to accept responsibility for the disaster, but has said Lapindo has said it will shoulder most of the massive clean-up and reconstruction cost, estimated to be about $A570 million, because of the Bakrie family’s “Indonesian values”.

Under a presidential decree issued last month – and criticised by many members of parliament – President Susilo Bambang Yudhoyono says his Government will pay the billions in infrastructure costs arising from the mud flow, including relocating transport links.

If that is the case, Santos’ costs should be contained, but the company has set aside $A89 million to cover its share of disaster remediation and concedes this could blow out further.