Well there's a few things with that I'm not quite on board with. Not powerful enough to take an underage Firebender? Torturing a Spirit? How is that done exactly? Also, physical torture isn't very Avatary. And the spirit special power thing - it would make more sense if there was a member in The Seekers who could read the spiritual energies of people instead. 

But actually, the thing pyroman suggested about the dates and such would make more sense. Though maybe that coupled with the energy reader thing could be an idea. They would have knowledge of his existence, and the means to track him down.