In April, a Dutch tourist exposed how lucrative the traffic division could be when he secretly filmed himself being shaken down for not wearing a helmet, then posted it on Youtube.

So when seven Australians were unwise enough to hire a buck's night stripper at a bar in Kuta earlier this year, they were creating an opportunity.

Police were probably tipped off by the bar or security guards. It's quite common for senior police to be silent partners in bar ownership in Kuta. They have a hand in the drug and sex trades. They associate with the street gangs and bouncers who act as enforcers and run protection rackets.

Money earned by police in these situations flows up and down the ranks, buying discipline from lower-downs and protection from higher-ups, according to Murdoch University academic Jacqui Baker, who has made a study of the black economy in the Indonesian police force.

If the bar owner did not get a cut of the $25,000 proceeds of the buck's night sting, then the superiors of the officers involved almost certainly did.