This latest incidence of mainstream lib media malfeasance is just another in a long list of failures to cover stories that embarrass their side. The biggest sin of the media is not that they tell lies but that they hide the truth.
What you have described is:
Bias by Omission:
Ignoring facts that tend to disprove liberal or left-wing claims, or that support conservative beliefs.
To catch this kind of bias you’ll have to be knowledgeable about the particular subject. If you know the various points of view on an issue, then you’ll recognize when one side is left out. Bias by omission can occur either within a story, or over the long term as a particular news outlet reports one set of events, but not another.
To find instances of bias by omission, keep abreast of the conservative perspective on current issues. See if that perspective is included in stories on a particular event or policy. If it’s not, you may have uncovered bias by omission.
See the list developed by FReepers years ago and found here: http://www.fairpress.org/identify.htm#omission