What is the test for determining whether a victim/witness in a murder case was a victim of retaliation for their testimony?

The People contend the trial court's interpretation of the special circumstance was erroneous. They maintain that the content of the victim/witness's testimony is irrelevant, that the evidence need only show the victim was killed in retaliation for the act of testifying for the special circumstance to apply. The issue here is one of statutory interpretation, which is subject to our independent review. (People v. Watson (1981) 30 Cal.3d 290, 300.)