Abuja - Nigeria's President Muhammadu Buhari on Monday said he was concerned about delays in prosecuting former public officials for corruption, warning it could harm his high-profile stance on graft."I am worried that the expectation of the public is yet to be met by the judiciary with regard to the removal of delay and the toleration of delay tactics by lawyers," he said."When cases are not concluded the negative impression is given that crime pays," Buhari told a summit examining the role of the judiciary in the overall drive against corruption."This certainly needs to change if we are to make success in our collective effort in the fight against corruption."Buhari, who was elected last year on a platform to tackle graft, has said "mind-boggling" sums of public funds were stolen over decades and has made recovering the money a central plank of his presidency.Most of those currently on trial are linked to the former administration of his predecessor, Goodluck Jonathan, and centre around an alleged $2.1bn "arms scam".Former national security advisor Sambo Dasuki is accused of overseeing a sprawling embezzlement scheme that saw money earmarked to fight Boko Haram diverted for political purposes.But there have been repeated delays and adjournments in that case and others, leaving Buhari without a single high-profile conviction since starting the crackdown in May last year.Buhari told the summit that government corruption cases "are not progressing as speedily as they should be... because the courts allow the lawyers to frustrate the reforms introduced by the law".Jonathan's main opposition Peoples Democratic Party has accused Buhari of a political witch-hunt, as most of those on trial are PDP members, supporters or linked to the former government.Buhari and his government have been criticised for disregarding the separation of powers of the executive and judiciary by keeping suspects in custody, despite courts having granted them bail.Last year, he said Dasuki and the detained leader of a Biafra separatist group should be detained because they had committed "atrocities" against the state, despite neither being convicted.