FBI agents have swarmed the headquarters of the recently-bankrupted solar energy firm Solyndra as part of a joint investigation by the justice and energy departments.

The agents executed search warrants Thursday at the facility in Fremont, California, but declined to say what specifically they were looking for.

Solyndra spokesman Dave Miller said the company was unaware of the search warrants and that he was surprised when he arrived at work and saw the agents.

Solyndra was once praised by President Barack Obama as a “testament to American ingenuity and dynamism” and received more than $500 million in federal loans.

Last week, the clean energy manufacturer said it was bankrupt, shutting its operations, and laying off 1,100 workers. The firm said it could not cut costs fast enough to keep up with Chinese solar panel makers.

Some U.S. members of Congress are calling for Solyndra’s CEO to testify about what went wrong. One California representative, Democrat Henry Waxman, said the CEO had told Congress just two months ago that his company was in a strong financial position.

Republicans have also questioned whether Solyndra received the loans unfairly because one of its key investors was also a major donor to the 2008 Obama presidential campaign.