Papua New Guinea's Police Minister Bryan Kramer says prosecuting high-profile corruption takes time.
Mr Kramer was taken to task in parliament by Moresby North East MP, John Kaupa, about a lack of results in corruption cases.
Mr Kaupa cited comments a year ago by the police commissioner that the force had investigation files on 40 MPs.
In response, Mr Kramer said that number had since been narrowed to around 20.
But he added that the process was not quick, especially after the police anti-fraud squad had been undermined by the previous government.
"To do a thorough, proper investigation, inot something go up inside lo wanpla day or wanpla week," he said.
"So it is frustrating. we are trying now, under the new government, the new prime minister (James Marape) to rebuild. So there's been some progress."
Meanwhile, PNG's former Prime Minister Peter O'Neill has made a court appearance regarding corruption charges.
Mr O'Neill was arrested last month as he returned to the country after spending months abroad.
Police from the anti-fraud unit are investigating the MP over his role in the state purchase of two generators from Israel in 2013 when he was prime minister.
Mr O'Neill, who was granted bail at $US1500, was arraigned at the Waigani Committal Court on Wednesday.
The matter has been adjourned for a month to allow police to complete investigations.