We discuss the connection between the construction of Bogomol'nyi boun
ds and equations in three dimensional gravitational theories and the e
xistence of an underlying N = 2 local supersymmetric structure. We sho
w that, apart from matter self duality equations, a first order equati
on for the gravitational field (whose consistency condition gives the
Einstein equation) can be written as a consequence of the local supers
ymmetry, Its solvability makes possible the evasion of the no-go scena
rio for the construction of Killing spinors in asymptotically conical
spacetimes. In particular we show that the existence of non-trivial su
percovariantly constant spinors is guaranteed whenever field configura
tions saturate the topological bound.