An Iowa grand jury is expected to hear testimony from Peregrine Financial Group's president next week as it begins considering alleged wrongdoing at the failed futures brokerage.

Russell Wasendorf Jr., Peregrine's president and the son of the brokerage's accused chief executive, has been subpoenaed by the grand jury and will likely testify next week, his lawyer told Reuters.

Russell Wasendorf Sr., Peregrine's founder and CEO, was arrested on July 13 on charges of lying to federal regulators in connection with an alleged massive financial fraud at the company. Prosecutors have said they expect to expand charges against him.

Peregrine, commonly known as PFGBest, filed for bankruptcy protection on July 10, one day after Wasendorf Sr. attempted suicide and left a note describing how he had bilked customers of more than $100 million over nearly 20 years.

Wasendorf Sr. said he had forged and intercepted financial statements that were mailed between U.S. Bank, where some Peregrine customer money was held, and the firm's auditors at the National Futures Association.