  Let $(X, g_0)$ be a complete, simply connected Riemannian manifold with
sectional curvatures $K_{g_0}$ satisfying $-b^2 \leq K_{g_0} \leq -1$ for some
$b \geq 1$. Let $g_1$ be a Riemannian metric on $X$ such that $g_1 = g_0$
outside a compact in $X$, and with sectional curvatures $K_{g_1}$ satisfying
$K_{g_1} \leq -1$. The identity map $id : (X, g_0) \to (X, g_1)$ is
bi-Lipschitz, and hence induces a homeomorphism between the boundaries at
infinity of $(X, g_0)$ and $(X, g_1)$, which we denote by $\hat{id}_{g_0, g_1}
: \partial_{g_0} X \to \partial_{g_1} X$. We show that if the boundary map
$\hat{id}_{g_0, g_1}$ is Moebius (i.e. preserves cross-ratios), then it extends
to an isometry $F : (X, g_0) \to (X, g_1)$.
