Malawian President Peter Mutharika’s longtime aide is wrapped in a corruption scandal after reports surfaced that he had become an instant billionaire in one of the world’s poorest countries. Ben Phiri, former special adviser and assistant to the president, is under investigation by Malawi’s Anti-Corruption Bureau after he apparently amassed a remarkable fortune in one year while earning a modest government salary, according to local media reports.

Phiri stepped down from his post last week following the accusations of wrongful self-enrichment, saying his resignation would allow investigators to carry out their probe. Anti-Corruption Bureau spokesperson Egrita Ndala said the department learned of Phiri’s alleged wealth through media reports, according to Malawi Nyasa Times.

More than 40 percent of Malawians live below the poverty line of $1.25 per day. The southeastern African nation ranked 160 out of 182 countries on the Human Development Index. Malawi consumer and human rights activist John Kapito has urged the public to scrutinize the monies declared by public officials, including Phiri and Mutharika, who have made their assets public according to the Malawian constitution.

“How did these people manage to have so much wealth when people are languishing in poverty?” Kapito told Malawi Nyasa Times in March. “We need to audit and continue monitoring the wealth [of politicians].”

Mutharika declared that he had about $10 million deposited in Malawi and U.S. banks, which puts him among Malawi’s billionaires. Phiri dismissed assertions that the president had exaggerated his wealth and denied comment on how Mutharika attained such a fortune. “He [the president] is operating within the law,” Phiri, the president’s aide at the time, told local radio Zodiak Broadcasting Station in March. “The law says he should declare, and it does not say that he should explain what he declared.”

The boggling wealth of Mutharika’s trusted aide also came under question. Phiri, who became the president’s assistant in 2007, challenged investigators to follow up on accusations of corruption against him “so that justice should prevail,” the Maravi Post reported in May.

“I am pretty sure I have served to my best of ability in all duties and responsibilities given. Unfortunately, there is a continuing disgruntlement within the society by me holding this position, and allegations made on wealth accumulated corruptly,” Phiri wrote in a resignation letter last month to the Malawi State House.