The Orange County, Calif. District Attorney’s Office this week raided the offices of Landmark Medical Management, whose president and CEO, Kareem Ahmed, was one of the largest individual financial backers of President Obama’s 2012 re-election effort.

Officials with the district attorney’s office on Tuesday morning executed a search warrant at Landmark’s office in Ontario, Calif., according to a source who works at Landmark and was present during the raid. The exact nature of the district attorney’s investigation is unclear.

“After they gathered everybody in the main area of the building, yeah, there was just an announcement that they had a search warrant, we weren’t to touch anything work related, we weren’t to touch any type of phones, we weren’t allowed to leave the area until we were identified and questioned,” the source, who spoke on condition of anonymity, told TPM.

According to the source, Ahmed was not present at Landmark’s office during the raid.

Landmark’s human resources manager, Ladonna Hieber, told TPM on Thursday that the company had “no comment on anything,” but that she was aware that this reporter was attempting to contact Landmark employees.

“My employees aren’t supposed to speak to you,” Hieber said.

The district attorney’s office also declined to comment on the raid.

“I’m not going to confirm or deny it,” Susan Kang Schroeder, chief of staff to the Orange County district attorney, told TPM on Thursday.

Ahmed had practically no history of political giving, and Landmark had little public profile, before he began giving large amounts of money to Obama, Democrats, and Democratic outside spending groups in 2012. Ahmed and his wife contributed well over a million dollars to Democratic efforts in 2012 — with the bulk of the money going to Priorities USA Action, the most prominent Obama-supporting super PAC.

But while Ahmed was and remains mostly unknown to the wider public, a TPM investigation last year found that both Ahmed and Landmark were familiar to people involved in California’s workers’ compensation system. People who know the industry and officials in the state told TPM that Landmark was one of several companies that had made millions of dollars in recent years by navigating a tricky corner of the state’s workers’ compensation system. Ahmed was an advocate of “compound drugs” — drugs whose ingredients have been combined, mixed, or altered by a pharmacist — and Landmark made money by buying accounts receivable from medical providers who prescribed compounded topical pain creams. In California, drug compounding was known as a physician profit center in the workers’ compensation system, and state lawmakers made a push in 2011 to remove some of the financial incentives associated with compound drugs in the system.

As a major donor in 2012, Ahmed rubbed shoulders with some of the most powerful people in the country — a fact he was proud to advertise.

“I hang out with governors, U.S. senators, Nancy Pelosi is a personal friend,” Ahmed told TPM in an interview last year.

After TPM contacted Ahmed last year, Bill Burton, the then co-head of Priorities USA Action, bristled at the attempt to learn more about Ahmed and his business.

“Not every person who is interested in investing in the direction of the country is looking to make themselves famous by doing it,” Burton told TPM at the time.

Ahmed wound up ranked 56th on The Center for Responsive Politics’ list of top disclosed individual donors to outside spending groups in the 2012 cycle, and he has continued to make political contributions into 2013. According to the Center, Ahmed has given over $30,000 to the Democratic Congressional Campaign Committee this year, and has cut checks for Rep. Mark Takano (D-CA), Rep. Bruce Braley (D-IA), and Rep. Karen Bass (D-CA), among others.

Neither Ahmed nor his attorney, Richard Brickman, returned a request for comment from TPM.

Suzanne Hodges contributed to this report.