  In this paper we compute the square root of the generalized squared total
angular momentum operator $J$ for a Dirac particle in the Kerr-Newman metric.
The separation constant $\lambda$ arising from the Chandrasekahr separation
ansatz turns out to be the eigenvalue of $J$. After proving that $J$ is a
symmetry operator, we show the completeness of Chandrasekhar Ansatz for the
Dirac equation in oblate spheroidal coordinates and derive an explicit formula
for the propagator $e^{-itH}$.
