Federal prosecutors have asked Parkland Memorial Hospital not to publicly release certain documents because of an ongoing investigation into "public corruption, money laundering and tax evasion," according to a document released Wednesday. The letter from the U.S. Attorney's office in Dallas to the Texas Attorney General asks that Parkland withhold records requested by several reporters under the Texas Open Records Act. The information requested directly relates to a Department of Justice ongoing investigation, the letter said. "We are currently conducting a criminal investigation which, in broad terms, involves allegations of public corruption, tax evasion and money laundering," the letter said. "As part of that ongoing investigation, we have directed Parkland to preserve and maintain certain records on our behalf." The letter, dated Aug. 2 and signed by assistant U.S. Attorney Walt Junker, said release of the documents could interfere or prejudice the investigation. Allison Sands, spokeswoman for the U.S. Attorney's office, said she could not confirm the letter or the investigation.