The question of whether journalists should have a privilege is a very hard one. Of course, you will seldom read, anywhere, that they should not, because journalists feel they are a special bunch.
This decision at least differentiates between already published material and information not published.
In Canada, the Supreme Court ruled last December that tv reporters have to provide "outtakes" of any videos taken which may depict a crime. So, not only is the televised version evidence, but everything else, too.
In the case which is referred to, it appears that someone may have made a statement relevant to the question of whether or not "ethnic cleansing" was planned. Was there a recording of the statement?
That would be very strong evidence, it seems to me.
And, presumably, we want war criminals to be convicted, so we want to be wary about offering
a privilege not to testify to categories of people.
On the other hand, we want a free press. And I presume there is some reality to the idea that people will not talk to the press so much, if they think they will hear their statements at an eventual trial, possibly leading to their imprisonment for life.
Generally, courts face this problem in the context of a criminal trial, as in this case. And so the free press issue seems more abstract, and the "obtain all the evidence" tack seems more pressing.
So courts usually privilege the need for evidence in a criminal trial above all other rights. An example is the case of U.S. v. Nixon, the Watergate case. There, Nixon relied on executive privilege, a doctrine that the executive cannot be forced to hand over its secrets to the judicial branch.
The court held that, while that might be true in some cases, a criminal trial and the issues of guilt or innocence took precedence over the executive's right.