LONDON (AFX) – US federal prosecutors are taking an active role in investigations into how beleaguered oil giant Royal Dutch/Shell over-stated its estimates for energy reserves, the Financial Times said.

The US Department of Justice in New York had asked that lawyers acting for Shell not publish a damning report into what went wrong, lest it compromise their own investigations, the newspaper said.

The Manhattan branch of the Department of Justice had been “influential” in making sure the report into Shell’s massive downgrading of reserves was not released in full, the paper said, citing unnamed sources “close to the investigation”.

The Department of Justice would not comment, but the London-based newspaper quoted a former US legal official as saying the action would likely have been taken to ensure potential witnesses did not have their testimony influenced.

Federal prosecutors had already been monitoring the case, but recently took a more active role, the report added.

Shell’s reputation has taken a battering in recent months as the massive reductions in stated reserves have been compounded by damning evidence that senior company executives tried to cover up the situation.

The group published internal memos and emails on Tuesday showing that executives were aware Shell was overstating the size of its recoverable energy reserves long before it told investors in January.

“I am becoming sick and tired about lying about the extent of our reserves issues and the downward revisions that need to be done because of far too aggressive/optimistic bookings,” former head of exploration and production, Walter van de Vijver, wrote in an email.