Journalism is not about digging until you find some kind of underlying "fact", there simply isn't time and what you're asking for could potentially be an extraordinary amount of work; journalism is about reporting what the reporter sees and what people tell them. Obviously it's incumbent on them to evaluate their sources, but not usually to write next to the sources' words the journalist's own opinion of the situation.
So for example in the Vegas situation, there will be a large number of official statements put out by various official bodies; or the reporter might call the hospital or a contact there; or they might go there and interview some people standing around.
But remember that this stuff does not cross the bar into what science or history would consider a fact. It's a snapshot of who's available and summary of what they said. There are always more people or organizations you could call for a quote, more people you could interview. And of course not all of them can or should be reported directly - there may be whistleblowers or vulnerable people to protect with a layer of indirection.
Journalism is not about digging until you find some kind of underlying "fact", there simply isn't time and what you're asking for could potentially be an extraordinary amount of work; journalism is about reporting what the reporter sees and what people tell them. Obviously it's incumbent on them to evaluate their sources, but not usually to write next to the sources' words the journalist's own opinion of the situation.
So for example in the Vegas situation, there will be a large number of official statements put out by various official bodies; or the reporter might call the hospital or a contact there; or they might go there and interview some people standing around.
But remember that this stuff does not cross the bar into what science or history would consider a fact. It's a snapshot of who's available and summary of what they said. There are always more people or organizations you could call for a quote, more people you could interview. And of course not all of them can or should be reported directly - there may be whistleblowers or vulnerable people to protect with a layer of indirection.