In this case, the defendant and his accomplice robbed a store. The State pursued a theory of accountability against the defendant and worked out a plea deal so the co-defendant, who was the principal who had the weapon, testified against him.
The defense was that the weapon wasn’t real, but rather, a BB-gun. The State presented another conviction where the co-defendant used a gun in an armed robbery to argue that, therefore, the co-defendant used a real weapon in this instance as well. The trial court permitted this use.
The appellate court affirmed the use of this type of evidence.
The case is People v. Clark.
http://www.illinoiscourts.gov/Opinions/AppellateCourt/2018/2ndDistrict/2150608.pdf