People v. Sullivan 

Defendant was convicted of aggravated robbery. After trial, two jurors wrote letters to trial court, one stating that he and other jurors were not sure of what jury instructions meant by the word "threatening". Other letter stated that juror did not believe that State proved guilt beyond a reasonable doubt, and alleged that jury deliberations were improper, including some jurors asserting that Defendant's decision to not testify was an indication of his guilt. These allegations, based on jurors' letters, cannot be verified by evidence other than jury's own motive, method, or process, and thus may not be considered to impeach jury's verdict. (STEIGMANN and COOK, concurring.)