You are missing the point.
Police said they were being fired at.
Couldn’t have been
NO GUN
Police said bomber shot himself in the throat with a gun
COULD NOT HAVE DONE IT
NO GUN
There have been a lot of misinformation about what police said or didn’t say from the news sources.
“Police would not confirm if Dzhokhar’s throat injury was the result of a suicide attempt or a police officer’s bullet.”
This is what I have seen in a few accounts.