  Consider the 3D Anderson model with a zero mean and bounded i.i.d. random
potential. Let $\lambda$ be the coupling constant measuring the strength of the
disorder, and $\sigma(E)$ the self energy of the model at energy $E$. For any
$\epsilon>0$ and sufficiently small $\lambda$, we derive almost sure
localization in the band $E \le -\sigma(0)-\lambda^{4-\epsilon}$. In this
energy region, we show that the typical correlation length $\xi_E$ behaves
roughly as $O((|E|-\sigma(E))^{-1/2})$, completing the argument outlined in the
unpublished work of T. Spencer.
