Brazilian regulators are reportedly investigating whether activist investor Nelson Tanure engaged in insider trading during his efforts to buy medical diagnostics company Alliar.

Last month, Nelson unveiled a 63.3% stake in Allier, formerly known as Centro de Imagem Diagnosticos, the result of a 20.50 Brazilian reais per share tender offer. The Brazilian businessman’s offer was first reported on November 18, which sent Alliar’s stock surging 22.5% in a single day.

Brazil securities regulator CVM is analyzing whether Tanure, during his talks with Allure between November and April, used non-public information derived from the negotiations to profit from significant market moves, according to documents seen by Reuters. This would constitute insider trading, with CVM manager Marco Antonio Papera Monteiro saying in the papers that the activist’s conduct suggested evidence of “potential crimes.”

Between November 18 and November 30, four investment vehicles controlled by Tanure, which already held a 29% stake in the company, sold 1.5 million common shares in Alliar for 25.4 million Brazilian reais ($5.3 million).

On December 22, Alliar said that shareholders could opt to sell their shares to Tanure’s vehicles only within two years, an announcement that plunged the stock on fears the tender was not necessarily due to the long time horizon. Regulators alleged that Tanure’s funds sold the shares knowing they would fall on market disappointment about the two-year window.

In a statement earlier in May, Tanure representatives said the transaction was “transparent.”

Tanure has a history with the regulator. The activist was fined 130 million reais ($26.7 million) in 2019 for “abuse of controlling power” at shipyard Verolme.