How do journalists use Twitter to break news?

Do journalists break news on Twitter before they break it on their employers' media outlet?

Or do they wait to break the news (say) on live TV first and then tweet it?

Or do they inform their colleagues running breaking news Twitter accounts for media organisations and then tweet on their own account?

Or does it go up as a flash on the website or on TV first before anything else happens?

I could go on with these hypothetical scenarios but the point is: what is the hierarchy of breaking news outlets these days for individual journalists?

I suppose to a certain extent it must depend on what the breaking news is and possibly differing organisational policies.

In other sort-of-not-really breaking Twitter news, Sky is going to install Tweetdeck on its computers so journalists can monitor Twitter and, no doubt, break news.

Maybe this will have an effect on my questions above?