Crummy Ending (SPOILERS OF COURSE)

The ship crashes, causes a fire, yet the imposters not only survived well, but dragged the dead human counterparts back to it to hide the bodies in it. Yet all that time, none of the earth security forces found the wreckage, which should have been easy since that would have been the starting point of the fire.

Then if the aliens are going to all this trouble to set a bomb off, why not just put it in a missile to begin with.