The latest additions came today, when the SEC filed charges against four more individuals and a hedge fund advisory firm (at which two of the individuals worked). From a press release:

The SEC alleges that Robert Feinblatt — a co-founder and principal of New York-based hedge fund investment adviser Trivium Capital Management LLC — and Trivium analyst Jeffrey Yokuty engaged in insider trading in the securities of Polycom, Hilton, Google and Kronos. The SEC further alleges that Polycom senior executive Sunil Bhalla and Shammara Hussain, an employee at investor relations consulting firm Market Street Partners that did work for Google, tipped the inside information that enabled the insider trading by Feinblatt and Yokuty on behalf of Trivium’s hedge funds for illicit profits of more than $15 million.

This brings the total number of defendants up to 27, and reports suggest that many more charges are yet to be filed.

More specifically, the SEC alleges that Bhalla, a Bay Area-based senior VP and general manager at Polycom (PLCM), tipped off an individual investor named Roomy Khan about Polycom’s Q4 2005 earnings. Khan allegedly traded on that information, and subsequently passed the insider info on to the Trivium execs. A similar exchange occurred the following quarter, except that this time Khan let the word slip to Raj Rajaratnam, the Galleon hedge fund manager whose actions touched off this entire investigation.

Khan is considered one of the government’s key witnesses in its Galleon investigation, after having been busted for insider trading herself.

The SEC also alleges that Khan told Trivium about a pair of impending private equity acquisitions: The Blackstone Group’s (BX) 2007 deal for Hilton Hotels, and Hellman & Friedman’s acquisition of Kronos that same year.

Finally, Hussain is alleged to have given Khan information about Q2 2007 earnings at Google (GOOG), which Khan then traded on and passed over to Trivium.

Overall, the SEC now has charged 27 defendants in the Galleon case.