RALEIGH, N.C. — North Carolina utilities regulators have released to the public more internal documents collected from Duke Energy Corp. in an ongoing investigation into its takeover of Progress Energy Inc.

The North Carolina Utilities Commission on Tuesday posted a second batch of emails and other information Charlotte-based Duke delivered to the regulators. Hundreds of pages were initially released two weeks ago.

The commission and Attorney General Roy Cooper demanded documents as they investigate Duke's surprise decision to change a key detail of its takeover even as regulators were considering approval – who would lead the combined company.

Progress Chief Executive Bill Johnson, who had been slated to become the top executive at the firm after the merger, was forced to resign by the Duke-controlled board within hours of the July 2 merger. The board then named Duke CEO Jim Rogers, who was supposed to be chairman of the utility, to replace Johnson.

The latest documents include a March 2011 letter to Rogers from an unidentified Duke shareholder criticizing the merger, saying Progress was mismanaged and that Duke was overpaying for the company.

Also in the documents was a May 15 email exchange between Johnson and Rogers over the departure of Catherine Heigel, a top Duke executive. Rogers said she was the second female executive to leave because of the pending merger, and Johnson responded that it was "a hazard of having high-quality employees."