With one mystery solved in what could be the biggest securities case before the Supreme Court in decades, the next imponderable is this: how many justices will participate and rule in the case?

The answer could decide whether or not the Court adopts a broad theory of securities fraud liability that would put law firms and other “third parties” in the cross hairs of investor class actions. That daunting prospect has drawn dozens of investor and business groups and lobbyists to both sides of the case of Stoneridge Investment Partners v. Scientific-Atlanta and Motorola.