At the end of the original series, Gendo Ikari seems to be diverging from their original idea, and to prevent this SEELE (committee?) sends Kaworu to NERV directly, aiming to make contact with the angel in terminal dogma. Ritsuko seemed to know the real identity, so why let it pass? (this is a comment not the question).
But how was SEELE able to do this (detect, find and recruit the fifth child)? It is supposed to be the case that no one knows where the angels come from.