According to you, since they failed to find the children, their search was ineffective.
Shouldn't cops be required to search until the missing child is found?
Wow, you are really grasping. Again, I'll note for you my point- it would seem that the police erred by not conducting a more thorough search of the vehicle. If you mean to ask about other cases in all recorded history, then the answer to your strawman of a question is, as you are aware, there are unsolved cases and each case depends on variables that the police should thoroughly investigate.