Prime Minister Dr Mahathir Mohamad believes his government would have a case against his predecessor Najib Abdul Razak “in a short while”.
He also said whether Najib would serve time in prison depends on the results of an investigation.
"If there is no case, we don't go for detention without trial," he was quoted as saying by Reuters.
Mahathir has pledged to investigate the 1MDB scandal if Pakatan Harapan comes to power. He has repeatedly accused Najib of siphoning funds from the firm, which the latter denied.
The 92-year-old politician said he would helm the nation for two years and would continue to play a role in the background even after he steps down.
"(In) an initial stage, maybe lasting one or two years, I will be the prime minister," he told a Wall Street Journal conference in Tokyo via a video link from Malaysia.
"I will play a role in the background even when I step down," he added.
As for Anwar Ibrahim replacing him as prime minister, Mahathir said the former opposition leader would need to seek a seat in parliament and then might be given a cabinet post, but would play the same role in the coalition as leaders of the other three parties in the alliance.
"I expect him to play the same role as the leaders of the other three parties.
“There will be no special powers given except as are given to ministers or deputy ministers or deputy prime ministers," he said.
Anwar, who is serving a five-year prison sentence, is scheduled to be released tomorrow after securing a royal pardon.
Meanwhile, Mahathir also said he welcomed foreign direct investment in Malaysia by China and other countries, but such investment must bring in capital and technology and provide jobs for Malaysians.
He also suggested that it would be necessary to limit immigration.
"Any country would like to restrain immigration from coming in large numbers," he said.
"We have the same problem. We need to restrict immigration and accept a certain number that we can deal with," he added.