Normally reporters can't be forced to name their sources, but in this case the name of the reporter's source IS THE EVIDENCE in a serious federal crime. If there is no other way to identify the source, a judge can make them talk. This is one case when the need to know outweighs the right to privacy. It would be the same if a reporter was an eyewitness to a murder.
So if the judge is trying to squeeze both, would not each of them try o hold out until the other blabs first?