A financial exchange operator says it was subpoenaed by a Chicago grand jury investigating missing cash at MF Global, the failed securities firm that was run by former New Jersey Gov. Jon Corzine.

CME Group Inc. said in an annual report Tuesday that the grand jury demanded documents and witnesses related to MF Global's failure. It said a separate subpoena came from the Commodity Futures Trading Commission, the lead federal agency investigating the case.

The grand jury probe had not been reported.

Regulators and authorities are trying to find out how $1.6 billion of client cash went missing from MF Global as it spiraled into bankruptcy.

CME Group runs exchanges where MF Global traded and was partly responsible for auditing the firm's books.

(Copyright 2012 by The Associated Press. All Rights Reserved.)