Quoting Phil Plait's very early speculation (http://www.slate.com/blogs/bad_astronomy/2013/02/15/breaking...):

"It appears to split, so I’m guessing the main mass split there. That’s not surprising; it’s happened with previous falls (like Sikhote-Alin). That means they could have disintegrated at different times, so there may be multiple places where pieces could fall."