Mossack Fonseca, the law firm at the heart of the Panama Papers affair, sold shell companies and held bank accounts that were used to help conceal bribes paid across South America, a Panamanian prosecutor alleged at a press conference on Thursday.

Rómulo Bethancourt, one of Panama’s organized crime prosecutors, is currently investigating Mossack Fonseca’s alleged role in an international corruption probe. The investigation, known as Lava Jato, is tracing dozens of companies that allegedly paid bribes to politicians and officials in Brazil in exchange for contracts with the state-owned oil company.

“We have a solid case,” Bethancourt said about his agency’s investigation of Mossack Fonseca, which began earlier this year. A separate investigation is ongoing into Mossack Fonseca and the Panama Papers.

Bethancourt told reporters that his office had identified two bank accounts in Panama that received “irregular” payments that were linked to Mossack Fonseca’s office in the Brazil.

Mossack Fonseca’s founders, Jürgen Mossack and Ramón Fonseca, have been detained since February in relation to the Lava Jato probe.

Mossack Fonseca’s Brazil operation “offered financial products aimed at hiding money that entered the Panamanian financial system,” Bethancourt said.

In response, lawyers for Mossack and Fonseca held their own press conference on Friday morning to respond to the prosecutor’s allegations.

The men’s lawyer, Guillermina MacDonald, said that the bank accounts mentioned by the prosecutor received legitimate administrative fees that were in no way illegal.

The bank accounts were closed after the release of the Panama Papers investigation by ICIJ and its media partners, MacDonald said. Contrary to the prosecutor’s claim, MacDonald said, the closing of the accounts was not due to the Lava Jato investigation.

Fonseca, Mossack and a third employee of the firm, Edison Teano, have been detained since Feb. 9. Mossack Fonseca’s former representative in Brazil, Maria Mercedes Riano, also remains in detention in Panama City.

Earlier this month, lawyers petitioned for the release of Mossack and Fonseca, insisting that their detention was unlawful. Panama’s criminal court has refused bail for the pair, citing the risk of flight and destruction of evidence.

Almost one year after it was first published, the Panama Papers data continues to be used by ICIJ partners in ongoing investigations, and to produce impact around the world. Among recent findings and responses:

Contributors to this story: Hamish Boland-Rudder