Swiss authorities have opened an criminal investigation in a Banco Santander hedge fund unit’s investments with convicted fraudster Bernard Madoff.

Geneva’s public prosecutor, Dario Zanni, said he was looking into whether then-Optimal Investment Services CEO Manuel Echevarria misled investors about his funds’ relationship with Bernard L. Madoff Investment Securities. Madoff is awaiting sentencing after pleading guilty earlier this year to running a $65 billion Ponzi scheme—$3.25 billion of it Santander client money.

“We have suspicions about” whether Echevarria did the due diligence Optimal claimed in its documents.,” Zanni told The Wall Street Journal. “We are not sure he was doing his job compliant with his duties.”

“We have two kinds of suspicion,” Zanni added. “Whether he knew that there was something wrong with Bernard Madoff, or he did not do the due diligence.”

Zanni said the criminal probe could take two years to complete. Echevarria left his post at Optimal last summer.

Santander has denied any wrongdoing in the Madoff matter. Spain’s second –largest bank offered clients who lost money in the scandal some compensation; almost all have accepted the deal.