The trial court reversibly erred in excluding the testimony of witnesses who observed defendant’s behavior before the shooting charged as murder, which defendant sought to use on the issue of his state of mind in connection with his theory of imperfect self-defense. A psychiatrist testified that he relied on summarized accounts of the excluded witnesses in forming his opinion that defendant had paranoid delusions. Defendant, who had actually been the victim of a home invasion robbery a year earlier, exhibited a false belief his home was currently being invaded, and other paranoid beliefs. The defendant was entitled to present the witnesses themselves to the jury. Here, the jury was deprived of hearing directly from among other witnesses, police officers who had personal knowledge of defendant’s bizarre behavior days before the crime.