It has been five years since the Nigerian government set up a new anti-corruption unit aimed at ending the country's reputation as one of the most corrupt on earth.
President Yar'Adua has vowed to fight corruption
The Economic and Financial Crimes Commission (EFCC) has been both hailed for bringing in some high-profile arrests, and also derided as a tool for attacking the government's political enemies.
What has the EFCC done since its inception?
The EFCC say they have secured 250 convictions, and recovered 500bn naira ($4.2bn) in assets from fraudsters.
Their two highest profile convictions are the former Police Inspector General Tafa Balogun, found guilty of stealing police funds while in office, and the former governor of Bayelsa State, Diepreye Alamieyeseigha, who jumped bail in the UK to avoid a money laundering charge.
The EFCC also convicted several advance-fee fraudsters known as "419ers". They say they have made it almost impossible for cyber criminals to operate in Nigeria. They believe that many are setting up shop in other West African countries.
Since the administration of President Umaru Yar'Adua was sworn in May last year the EFCC has arrested and charged eight former state governors after their immunity from prosecution ran out.
The daughter of former President Olusegun Obasanjo has also been charged with corruption.
President Yar'Adua has often said there would be no "sacred cows" in the war against corruption.
Is Nigeria any less of a corrupt place now than it was?
While supporters of the EFCC say an unequivocal "yes", other commentators have a less positive view.
Many say the EFCC is a tool of the government to deal with enemies who have opposed them, rather than changing the system that allows corrupt politicians access to vast budgets from oil revenues.
The politicians and public servants they successfully convicted had angered former President Obasanjo, commentators say, and some of the pending cases are also politically motivated.
While prosecuting corruption in a place like Nigeria will always be difficult because of the myriad of competing political interests at work, money is still being drawn out of local, state and federal treasuries and shared between a political elite.
How serious is Nigeria's government about political reform?
At every stage President Yar'Adua has stressed his commitment to anti-corruption and the rule of law.
But some commentators have questioned the government's resolve.
As soon as the EFCC arrested and began a prosecution of former Delta State Governor James Ibori, a key ruling party donor, the head of the agency, Nuhu Ribadu, was transferred out of his job.
Other people have a bleak view of the prosecutions of the eight former governors.
It could go one of two ways, they say.
The first would follow the course of the other EFCC prosecutions: the accused if found guilty would serve short jail sentences and have some assets seized.
In the past the EFCC's lawyers have said they will not rule out "plea bargains" for corruption cases, where the accused can give back money they have taken to avoid jail.
The second scenario is that the cases could well be dismissed on technicalities, before the evidence ever comes to court.
What is in the future for the war against corruption?
After Mr Ribadu was sent on study leave, there has been much speculation in the Nigerian media about the EFCC's future.
Some commentators have suggested that the EFCC might be merged with the country's other anti-corruption agency the Independent Corrupt Practices Commission (ICPC).
This unit would then be lead by a former inspector general or judge.
But sociologist and criminologist Professor Epannibi Alemika of the University of Jos, says that there will be no progress until the incentive for political elites to steal is removed.
The trouble is, he says, that there is no other way of making money in Nigeria other than stealing money from oil revenues.
And unless the elite is placed under a tax system where they must justify their earnings, they will continue to steal.
"Law enforcement will always be one step behind them in their schemes," he says.