Can a defendant be held liable for failing to prevent a witness from testifying?

Here, it is apparent that appellant intentionally interfered with the trial process with this incredibly transparent ploy. By any standard of proof, appellant's conduct was intentional and designed to prevent a witness from testifying. The absence of a forfeiture rule covering this sort of conduct would create an intolerable incentive for defendants to bribe, intimidate, or even kill witnesses against them. ( Giles v. California (2008) 554 U.S. ----, ----, 128 S.Ct. 2678, 2686, 171 L.Ed.2d 488, 499.)