North Carolina utilities regulators said Wednesday they have hired a former federal prosecutor with experience digging into corporate affairs to reveal whether regulators were misled ahead of a takeover that created America's largest electric company.

The North Carolina Utilities Commission said it has hired Anton Valukas and the Jenner & Block law firm, which he heads in Chicago. The ex-prosecutor and his firm are tasked with investigating what happened before regulators approved Charlotte-based Duke Energy Corp. taking over Raleigh-based Progress Energy Inc.

State law allows the costs associated with the utilities commission's investigation to be charged to Duke Energy and its shareholders rather than allowing the company to pass them along to its 3.2 million North Carolina customers.

A Duke Energy spokesman said the company was cooperating with regulators in their investigation.

The company on Wednesday separately sought to begin passing along to Carolinas energy consumers the first $89 million of $650 million in merger-related savings promised over the next five years. If that is approved, the average residential customer in North Carolina and South Carolina could save between 80 cents and 92 cents a month beginning in September.