  We prove the functional equation for the twisted spinor L-series of a
cuspidal, holomorphic Siegel eigenform for the full modular group of genus 2.
It follows from a more general functional equation, valid for Rankin
convolutions of paramodular cuspforms. A non-vanishing result for
Fourier-Jacabi coefficients of the eigenforms in question is the central pillar
of the deduction of the former from the latter functional equation.
