Nigerian anti-graft officials visited the offices of Dangote Industries Ltd, controlled by billionaire Aliko Dangote, as part of an ongoing probe into Godwin Emefiele, the former head of the country’s central bank.

An official at the Economic and Financial Crimes Commission confirmed the visit to the Lagos headquarters of Africa’s richest person. The official, who declined to be identified, said the commission’s team was looking into foreign exchange dealings with the central bank under Emefiele, who was arrested in June on charges including fraud.

Officials at Dangote did not immediately respond to requests for comment.

The probe into Emefiele, who has denied wrongdoing, levels a number of claims against him including setting up hundreds of unauthorized offshore bank accounts, one of which in the UK that alone contained 543 million pounds ($690 million).

The investigation, which was opened in July on the orders of President Bola Tinubu, also accused Emefiele of manipulating the naira.

From 2015 until it was scrapped in June, the central bank under his leadership operated a complex foreign exchange regime designed to shore up the naira by limiting the amount of dollars available from official sources. This made the Nigerian currency look stronger on the official market, even as it weakened on the unofficial parallel market.

Tinubu used his first speech after taking office in May to criticize the policy, which he said encouraged arbitrage.

That mismatch meant that entities able to get dollars at the official rate could profit enormously by a so-called round trip where they converted into naira at a rate that offered 70% or more in local currency.

The president suspended Emefiele in June and the former central bank chief was arrested shortly afterwards and taken into custody. He was released on bail last month.