In the case of Giles v. California, the U.S. Supreme Court ruled in 2008 that a defendant's Sixth Amendment right to confront witnesses against him is not violated when hearsay evidence is admitted at trial if it falls under an exception for statements made by unavailable witnesses who had been intentionally killed by the defendant, but only if the prosecution can show that the killing was done with intent to prevent testimony. The decision overturned a ruling from California’s Supreme Court which allowed such testimonies without requiring proof of intent to silence witness testimony. This case involved Dwayne Giles, who was convicted for murdering his ex-girlfriend Brenda Avie based on her previous statements to police about his violent behavior towards her.

In the dissenting opinion for Giles v. California, Justice Breyer argued that a defendant forfeits his Sixth Amendment right to confront witnesses against him if he intentionally prevents them from testifying, regardless of whether he intended to prevent their testimony at trial specifically. He believed this interpretation was more consistent with historical common law and would better serve public policy by deterring witness tampering. The majority's narrower interpretation requiring specific intent to prevent testimony at trial could allow defendants who intimidate or murder witnesses but do not specifically intend to stop their future court appearances, escape punishment for their crimes due to lack of evidence. This could undermine the justice system and potentially encourage such behavior in criminals aware of this loophole.