Federal prosecutors investigated Galleon Group hedge fund founder Raj Rajaratnam on suspicions of insider trading more than a decade before he was charged with securities fraud, the Wall Street Journal reported, citing legal filings.

However, the prosecutors were unable to prove their suspicions, the paper said.

The investigation stemmed from suspicions that arose in the 1990s within chip maker Intel Corp that Rajaratnam was receiving tips from an Intel insider.

Intel could not immediately be reached for comment by Reuters outside regular U.S. business hours.

The Sri Lankan-born billionaire was arrested on October 16 and accused by prosecutors of generating millions of dollars of illegal profits in the largest U.S. hedge fund insider trading case on record.

Rajaratnam has denied the charges.