Do you have a link for that? (other than Kos and the DUmmies?)
Posted elsewhere and it's from ABC News which ain't much better than KOS, but:
This article states that: "Oscar Grant took a cell phone picture of BART officer Johannes Mehserle holding a Taser, just moments before he pulled his gun and shot and killed Grant on a BART platform on New Year's Day 2009."
The same information made several major news services.
I haven't seen the picture(s) in question but believe that they were used in court as well.
So anyone who believes the story that Mehserle mistook weapons when he clearly swapped them is an idiot. a boot-licker or both, plain and simple.