D, along with eighteen co-defendants, was charged with numerous counts of conspiracy to distribute cocaine. The jury was unable to reach a verdict as to D, and the court declared a mistrial as to him. D was retried. Jack Ventimiglia's residence appeared to be the main terminal for considerable cocaine distribution. Ventimiglia was arrested and testified for the government against several of his associates including D. Ventimiglia is a cocaine addict, and his testimony at the trial was characterized by the district court as the words of a 'loose cannon.' On cross-examination, D was able to expose Ventimiglia's cocaine addiction, his claimed lack of memory, his uncertainty as to details, and several inconsistencies in his testimony. The court admitted the testimony. In ruling on D's motion for a judgment of acquittal, the district court stated that Ventimiglia's testimony alone would not support a guilty verdict; but the motion was denied as P had introduced, apart from Ventimiglia's testimony, substantial circumstantial evidence that would tend to support the fact that D was, in part, a seller. D was convicted and appealed. D argued that Ventimiglia was unable to satisfy the personal knowledge requirement of Rule 602 and the testimony should not have been admitted.