The exterior view of bankrupt Solyndra is seen in Fremont, Calif., Sept. 16. (AP)

A four-year investigation has concluded that officials of the solar company Solyndra misrepresented facts and omitted key information in their efforts to get a $535 million loan guarantee from the federal government. 

The company's collapse soon after getting federal backing provided ammunition to lawmakers and other critics who portrayed President Obama's economic stimulus program as wasteful government spending. The company's failure likely will cost taxpayers more than $500 million. 

The report by the Energy Department's inspector general was released Wednesday. It's designed to provide federal officials with lessons learned as it proceeds to grant billions of dollars in additional loan guarantees. The inspector general found fault with the Energy Department, describing its due diligence work as "less than fully effective." The report also said department employees felt tremendous pressure to process loan guarantee applications. 

In the end, however, the inspector general said the actions of the Solyndra officials "were at the heart of this matter." 

"In our view, the investigative record suggests that the actions of certain Solyndra officials were, at best, reckless and irresponsible or, at worst, an orchestrated effort to knowingly and intentionally deceive and mislead the department," the IG's report said. 

A federal loan guarantee program for energy projects was established in 2005 during President George W. Bush's administration. Four years later, the Democratic-led Congress passed an economic stimulus bill that substantially expanded the program. In the ensuing two years, the department disbursed more than $500 million to Solyndra, but in September 2011, the company laid off 1,100 employees, ceased operations and filed for bankruptcy protection.