[meteorite-list] Where's the other one?

[Meteorites USA]

Hi Listees,

We've all read the articles and seen the photos of P/2010 A2 (the 
"asteroid" impact) Possibly the first ever witnessed and photographed 
asteroid collision in the asteroid belt.

http://www.skyandtelescope.com/news/82074747.html
http://www.cfa.harvard.edu/mpec/K10/K10A32.html
http://www.newscientist.com/article/dn18415-trail-of-dust-may-point-to-fresh-violence-in-asteroid-belt.html
http://www.astroengine.com/?p=7086

I have a few questions...

If the 110,000 mile long trail of debris is the result of two asteroid 
colliding, where is the other one? Shouldn't there be two trials of 
debris visible? Wouldn't each asteroid have it's own debris trail? Or is 
the trial we are seeing in fact from both because they are not far 
enough away from each other yet to make two distinct trails?

Regards,
Eric Wichman
Meteorites USA