A guy says he has a tape of him and Britney Spears having sex. I am sure you can hear such stories at the pub every day. But how does this get to the news?
Get someone to report it on the news. Or have such a tape.
In this case, proof of the claim.
That’s nothing.
I have a video of an alien using a rectal probe on Britney Spears, Paris Hilton and Lindsey Lohan. 
It should only be news if the journalist has actually seen the tape surely?
Nay, if you can pitch it properly the rumor is sufficient, in this case, to become newsworthy. I ain’t saying it’s right…just that it’s real.
We’d all eb better off if bloggers and such insisted on seeing the facts or evidence prior to running with such but they don’t so we’re not better off.
More seriously, if you make a (preposterous) claim about someone and they react, then you can report the claim and the denial as news.