AUSTIN (December 11, 2012)—Gregg Cox, the director of the Travis County district attorney’s public integrity unit, said Tuesday he has opened an investigation into the state's troubled $3 billion cancer-fighting agency.

Cox told The Associated Press on Tuesday that the investigation is underway into the Cancer Prevention and Research Institute of Texas.

The agency is also under investigation by the Texas attorney general's office after an $11 million grant to a private company did not receive the proper review.

Cox says his office is starting an investigation not knowing "what, if any, crime occurred."

Cox's unit prosecutes crimes related to the operation of state government.

Earlier Tuesday, the institute released a resignation letter from its Executive Director Bill Gimson, who headed the agency since it launched in 2009, but fell under mounting criticism over the recent disclosure that the $11 million award to a private company was never reviewed.

Gimson wrote that he had been "placed in a situation where I can no longer feel effective."

The agency's board must still approve his request to resign.

Only the National Institutes of Health doles out more cancer research dollars than the CPRIT.