The Sixth Amendment guarantees, among other things, that an accused person "shall enjoy the right . . . to be confronted with witnesses against him." The Supreme Court in 2004, in an opinion written by Justice Antonin Scalia, also applied that standard to "testimonial statements" in criminal trials, but it left unclear what would be considered "evidence," which does not require being able to cross-examine one's accuser, and what would be considered "testimony," which does. What about 911 calls?