The Wall Street Journal reports that Cynthia Cooper, the internal auditor who unearthed WorldCom's alleged accounting fraud, is co-operating with the US Justice Department. Her account of what transpired at the company is thought to conflict with WorldCom's own version of events.
Federal prosecutors are still gathering evidence in order to make a decision whether to bring criminal charges against the company and some of its executives.
Ms Cooper is believed to have told investigators that she discovered the alleged £2.5bn fraud herself and took it to WorldCom's former chief financial officer, Scott Sullivan. Cooper alleges that she then went to the head of WorldCom's audit committee after Sullivan put up some resistance about the matter. Even then there was a delay before the matter was brought before the public. WorldCom executives claim that Ms Cooper came across the alleged fraud during a routine audit and that they took immediate steps to get to the bottom of the matter.
The company has already been charged with fraud by the US Securities & Exchange Commission (SEC) and is also under investigation by Congress. The SEC has complained that they still await a credible explanation of exactly what happened from the company.