Police officers, after being placed in different states of physical effort, viewed videotapes of an aggressive or non-aggressive offender. Test monitors noted whether the officers did or did not shoot at the offender. Next, via a questionnaire, they investigated the officers' judgment of the offender's aggressive impression. Finally, also via a questionnaire, they examined the extent to which the officers were able to accurately describe the offender and other features of the situation. The findings of this experiment confirmed the hypotheses that physical effort will result in a decrease in aggression towards aggressive offenders and that this decrease will be caused by an incorrect judgment of the aggression of aggressive offenders, not by an impaired perception. Increased aggression will occur when an aggressive impression has been made. Notes, table, figures, references