Lagos - It would be easy to believe that President Muhammadu Buhari is winning the war against corruption since his landmark election victory nearly a year ago.
Hardly a week goes by without the Economic and Financial Crimes Commission (EFCC) announcing new arrests and investigations to add to the prominent politicians already in the dock.
But the longer the cases already brought to court drag on, the clearer it becomes that a potential setback could prevent Buhari from securing the convictions he has promised - and Nigerians demand.
Call it "the Goodluck Jonathan alibi".
Even before the final election results were announced last March, Jonathan conceded defeat, accepting the inevitable that Nigerians had for the first time in the country's history ousted an incumbent president.
Then, in a strategy designed to keep the peace and avoid a renewed flare-up of election-linked violence, Buhari extended an olive branch to the ousted leader.
"President Jonathan has nothing to fear from me," he pledged in his acceptance speech, indicating he wanted to draw a line under the past.
Certainly, the EFCC has not implicated the former head of state in any of its ongoing investigations.
But his glaring absence is increasingly posing problems for state prosecutors as the preliminary stages of cases are heard in court and trials get under way.- 'Indispensable witness' -
Take Olisa Metuh, the spokesman for the People's Democratic Party (PDP), who is facing money laundering charges.
According to the prosecution, he received a share of millions of dollars earmarked for buying weapons and equipment for troops fighting Boko Haram that were allegedly diverted to prominent PDP members.
The money, it is claimed, was to fund Jonathan's re-election campaign.
But Metuh says he was only acting on Jonathan's orders and last week argued he should be acquitted because the former president has not been called to the stand.
"The former president forms an indispensable witness," Metuh's lawyer Onyechi Ikpeazu told AFP.
Without Jonathan's testimony, the state, which has closed its case after several witnesses, hasn't presented enough evidence to convict Metuh, he argued.
"We are saying the failure to investigate what really amounts to an alibi is fatal to their case," Ikpeazu added.
A judge is expected to rule next week on Metuh's "no-case" submission, which if it favours the PDP official may set a disastrous precedent.
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One lawyer working for Sambo Dasuki has also hinted at pursuing a similar defence.
Dasuki, who is accused of diverting the weapons procurement cash through his office via bogus defence contracts, has himself said he was only doing the bidding of the then-commander-in-chief - Jonathan.
"The national security advisor will normally carry out the instructions of his president," Dasuki's lawyer Ahmed Raji said in January.
"You cannot talk about this matter without talking about President Jonathan."- Political decision -
For his part, Jonathan, who no longer has immunity from prosecution, has kept mum.
"These issues of corruption and misuse of funds are being investigated before the court and I wouldn't want to compromise the implementation of our laws," he told France 24 in an interview in January.
"I would not want to make comments to appear that I am making a debate with the current president."
If the "Goodluck Jonathan alibi" works, many high-profile accused could potentially walk free, dealing a serious blow to Buhari's pledge to root out endemic corruption and impunity.
Buhari has previously warned the country's monied elite it was "no longer business as usual".
But with Nigeria in economic crisis as a result of the collapsing price of oil, analysts say Buhari can ill afford to alienate Jonathan and his allies, even if it threatens success in court.
"It's a political decision," said Clement Nwankwo, executive director of the Abuja-based Policy and Legal Advocacy Centre, which promotes greater government transparency and better governance.
"The question is, does the Buhari administration have the political capital to push through getting Jonathan to testify?"
A diplomatic compromise could then result in watered-down sentences - if any at all. How ordinary Nigerians forced to live with the effects of corruption would react then remains to seen.
"I don't really think all of these people will end up with a trial, and I don't think they'll end up getting jail time," said Manji Cheto, sub-Saharan Africa analyst at London-based Teneo Holdings.
"It's one thing to promise cracking down on corruption but it's another thing for people to see tangible evidence of your crackdown."