Indonesian police say they are preparing to file a brief recommending up to 13 people be charged over the country's "mud volcano" disaster in heavily populated East Java.
But it's unclear whether the catastrophe – linked to one of Indonesia's most powerful families – will ever make it to court, with the chief prosecutor saying he believed the "mud volcano" was a natural disaster, and not man made.
It has been almost a year since an unstoppable flow of mud burst through the earth during deep drilling at a nearby exploratory gas well – linked to the family of Indonesia's Public Welfare Minister Aburizal Bakrie and also part-owned by Australian company Santos.
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.
The mud continues to flow at a rate of 160,000 cubic metres each day – with no end in sight. All efforts to stop it have failed.
As the May 29 first anniversary of the disaster nears, police said they were preparing to file their report "very soon", recommending either negligence or deliberate act charges against those involved in the drilling.
It will be the third time they have handed the paperwork to prosecutors, who have twice returned it seeking further information.
East Java police investigator Supriyadi said police had gathered enough evidence to mount a case of criminal negligence over the drilling of the well. "According to investigators, we have a criminal case of a negligence in the drilling," Supriyadi said.
Police will recommend charges under both the criminal code and environment management laws, with penalties ranging up to 15 years' jail, or a 750 million rupiah ($A105,000) fine for a deliberate act of pollution which causes loss of life.
Thirteen people were killed in November when a gas pipeline under the mud cracked under pressure and exploded.
"We will put both deliberate act and negligence articles in the charges, but to tell you the truth it is leaning more to negligence," Supriyadi said.
"It is almost impossible that it was a deliberate act. According to the investigators we have sufficient evidence for a trial, but the dossier is still incomplete based on the advice of the prosecutors."
Police say they have questioned 59 witnesses and an extra 16 experts in geology, the environment, water management, land degradation and meteorology.
"Yes it has been a long time, almost a year," Supriyadi said. "There are obstacles, like the dossier going back and forth from police to the prosecutors. According to the investigators, this is man made, triggered by the drilling. We are going to file it again soon, very soon."
But East Java's provincial prosecutor Mulyono said he personally believed the disaster was a natural phenomenon. "If the question is when (the charges will be filed), I don't know," Mulyono said.
"But as long as the police have not fulfilled the items the prosecutors want, it's not going to happen. When they file it again we will have to study it. My personal opinion is this is natural, not man made, because you know, negligence can be overcome, but not this. They are trying to divert the mud south but it keeps going north, so that's God's willing. We will process it (the case) but I don't know whether it will reach the court."
Santos, which owns a non-operating 18 per cent stake in the venture, has set aside $A89 million for its share in repairs and losses from the disaster. It is not under police investigation.