Activist investor Pentwater Capital Management LP is Turquoise Hill's largest shareholder after Rio with a 9% stake. In its class action complaint filed in the United States District Court for the Southern (NYSE: SO ) District of New York on March 16, Pentwater said that senior executives of Rio Tinto and Turquoise Hill "repeatedly assured investors that progress on that development was on plan and on budget and that the deadline for achieving sustainable first production when the mine would begin generating cash flows remained intact." "In reality... the underground expansion project was many months behind schedule and hundreds of millions of dollars over budget," it said in the 160-page filing.