There are probably hundreds of pics on the web of cops who allowed a knife attacker to get too close and they aren’t pretty.
Mythbusters did an episode on knife v. gun and discovered that a guy with a gun did not want to try and defend himself against a knife wielder when the guy with the knife was within about 20 feet. The gun guy was likely to be stabbed almost every time (about 80% of the time) before he could get off a shot in defense that would hit the guy with the knife. It was even worse when the knife guy was closer. They were quite surprised at their findings. This was with the gun guy expecting and watching for the attack!
The only difference between this and the police shooting was the gun guy in the Mythbuster’s episode was the gun guy was starting with a holstered gun and the police had their guns already out.