Raj Rajaratnam, the hedge-fund billionaire charged as part of a vast insider-trading case, surfaced in an earlier, separate probe into U.S. fund raising by a Sri Lankan terrorist group, people familiar with the probe said.

As part of that investigation, federal agents said they uncovered documents showing Mr. Rajaratnam, founder of the Galleon Group, was among several wealthy Sri Lankans in the U.S. whose donations to a Maryland-based charity made their way to the Liberation Tigers of Tamil Eelam, these people said. The LTTE,...