Weapon focus refers to a factor that affects the reliability of eyewitness testimony. Where a weapon is used during a crime, the weapon is likely to divert the witness's attention to the weapon that the perpetrator is holding and this affects the ability of the witness to concentrate on the details of the crime. The visual attention given by a witness to a weapon can impair his or her ability to make a reliable identification and describe what the culprit looks like if the crime is of short duration.
The focused attention that an eyewitness pays to the weapon that the perpetrator holds during the commission of the alleged crime forms the basis of this concept. The proponents of this view believe that all the visual attention of the eyewitness gets drawn to the weapon, thereby affecting the ability of the eyewitness to observe other details. Chief Justice Rabner acknowledged the results of a meta-analysis undertaken by Nancy Steblay on this topic. In this meta-analysis, data from various studies on this subject was collected and analyzed to determine if the presence of a weapon may actually be a factor affecting the memory or perception of an eyewitness to a real crime. Of the 19 weapon-focus studies that involved more than 2,000 identifications, Steblay found an average decrease in accuracy of about 10 per cent when a weapon was present. In a separate study, half of the witnesses observed a person holding a syringe in a way that was personally threatening to the witness; the other half saw the same person holding a pen. Sixty-four per cent of the witnesses from the first group misidentified a filler from a target-absent lineup, compared to thirty-three from the second group. Weapon focus can also affect a witness's ability to describe a perpetrator. A meta- analysis of ten studies showed that "weapon-absent condition[s] generated significantly more accurate descriptions of the perpetrator than did the weapon-present condition". Thus, especially when the interaction is brief, the presence of a visible weapon can affect the reliability of an identification and the accuracy of a witness's description of the perpetrator.