I’ve just posted a comment where I researched all the incidents here. Mark Venturi appears to be suicide-by-cop, and Khiel seemed to be mentally ill and told police he had a gun while concealing the hairbrush as though it were a gun. The real fucked up part of Khiel’s case is that the cops then killed his brother too in apparent retaliation for the backlash from killing Khiel. ACAB.
The case definitely involved an incident of “police thought they saw a firearm that didn’t exist”, it just doesn’t say anywhere in the Wikipedia article that what they thought they saw was actually another object. Maybe it’s true, but it’s a piece of trivia from an external article that just didn’t make the Wikipedia page.