Yesterday, we noted that the FBI’s (leaked) announcement that it was investigating four of the financial titans at the center of the current financial crisis was remarkably short on details.

But the Washington Postfollows up today with more detail on one of those companies: AIG. Federal investigators have been “scrutinizing” AIG since March, the Post reports. The investigation is advanced enough that they’re interviewing witnesses – but at a “delicate stage,” the sources tell the Post. The focus is on “whether the insurance giant knowingly concealed mammoth losses that helped lead to the company's $85 billion federal bailout this month.” An AIG spokesman told the Post the company wasn’t aware of the probe, but said it would cooperate.

The piece makes no mention of the other three companies cited in the FBI leaks Wednesday – Fannie Mae, Freddie Mac and Lehman Brothers. We’ll let you know if other details emerge.