What is the test for a jury to determine a "special circumstance" in a murder case?

During deliberations, the jury sent out a note stating it could not decide the special circumstance and needed clarification, specifically, "Does it have to be the primary reason or partial reason?" After input from counsel, and relying on People v. Michaels (2002) 28 Cal.4th 486 (Michaels), the trial court proposed to reread CALCRIM No. 720 and then add language telling jurors it was not necessary that financial gain have been the only purpose, or even the primary purpose, for the killing.