Media are pawns of the extremists

Because they're so willing to report any rumor as fact. This time they blew it, as detailed by Multi-National Force Iraq:

Extremists using false media reporting to incite sectarian
violence

BAGHDAD, Iraq – Friday, news media reported a mass killing
in a village near Salman Pak where 20 men were allegedly found beheaded.
It now appears that the story was completely false and fabricated by unknown
sources. Upon learning of the press reports, coalition and Iraqi
officials began investigating to determine if the reports were true.
Ultimately it was concluded the reports were false. Anti-Iraqi
Forces are known for purposely providing false information to the media to
incite violence and revenge killings, and they may well have been the source of
this misinformation.

This is why you can't trust all you hear on the news reports, and why many in Washington are being intimidated toward an early pullout.