It didn't magically disappear, some rando picked it up and walked away with it while the cops were dealing with the guy.
There are videos of the whole thing online, you should watch them. Fuck the police but let's be honest about that particular situation.
Not justifying the cops shooting up everything, but he 100% had a knife and was acting dangerously. They tried using tasers first which didn't work.
There are videos. People who are saying that a man was murdered just over couple bucks of fare are purposefully leaving out some crucial details. I get it, but it's dishonest.