Taylor (D) was indicted for attempted murder. Well in advance of the trial, the prosecution filed a motion requesting a list of D's defense witnesses. D identified his two sisters and two men who did not testify. On the first day of trial, D was allowed to amend his answer by adding the names of Derrick Travis and a Chicago Police Officer, but neither of them testified at trial. On the second day of trial, D made an oral motion to amend his discovery answers to include two more witnesses, Alfred Wormley, and Pam Berkhalter. Counsel for D represented that he had just been informed that those two parties had probably seen the entire incident. Counsel acknowledged that he knew of the witnesses but had been unable to locate Wormley. The Judge, after noting that the witnesses' names could have been supplied even if their addresses were unknown, directed counsel to bring them in the next day, at which time he would decide whether they could testify. Wormley testified that, prior to the incident, he saw Jack Bridges and his brother with two guns in a blanket, that he heard them say 'they were after D and the other people,' and that, on his way home, he 'happened to run into D and them' and warned them 'to watch out because they got weapons.' Wormley acknowledged that he had first met D 'about four months ago' (i.e., over two years after the incident). He also acknowledged that defense counsel had visited him at his home on the Wednesday of the week before the trial began. His testimony rather dramatically contradicted defense counsel's representations to the trial court. The judge found a blatant and willful violation of the discovery rules. The trial judge concluded that the appropriate sanction for the violation of the discovery rule was to exclude the testimony of Wormley. A jury convicted D of attempting to murder Jack Bridges. The conviction was supported by the testimony of Bridges, his brother, and three other witnesses. The incident was witnessed by 20 or 30 bystanders. That conviction was affirmed, and the Illinois Supreme Court denied leave to appeal. The Supreme Court granted review. D contends that the Sixth Amendment bars a court from ever ordering the preclusion of defense evidence as a sanction for violating a discovery rule. Alternatively, he contends that even if the right to present witnesses is not absolute, on the facts of this case, the preclusion of Wormley's testimony was constitutional error.