Why do only certain crimes get any attention?

While catching something about the missing Salt Lake kid on the news yet again, it got me thinking. Kids disappear all over America every day, why does one case become a nationwide media circus while others only get a paragraph in the back of their local paper? This goes for all crimes in general. Why do some events become big, national news while hundreds of others just like it slip by unnoticed?

(Mods, I have no idea where this question fits best. I can see it just as easily in IMHO, GD, or even the Pit. Please close/move as you see fit.)

Many times, a very unusual or, while I hate to use the word, interesting aspect of a crime catches the public’s attention. In the Smart case, it is that the girl was abducted from her home while her family slept (very rare) as well as the added excitment of the little sister witnessing the abduction. Also, it can depend a lot on the dedication of the victim’s family in seeing that the media coverage is extensive. I’m thinking specifically of the Chandra Levy case here, where no one was taking the parent’s missing person report seriously until they went to the media with the hint of a scandal. All of a sudden–BOOM–it’s all over the news.
There’s not any one reason that covers all cases of course, but I think in most “infamous” cases, you’ll find one of the following
*a famous victim or suspect (Robert Blake, OJ)
*very unusual or rare situation (Smart, JonBenet)
*“Interesting” facets of the crime (Gacy’s clown gig, Yate’s killer-mom act x 5 )
*It falls into a current “pet crime” catergory (home invasions, terrorism)