  We consider a D=4 two-twistor lagrangian for a massive particle that
incorporates the mass-shell condition in an algebraic way, and extend it to a
two-supertwistor model with N=2 supersymmetry and central charge identified
with the mass. In the purely supertwistorial picture the two D=4 supertwistors
are coupled through a Wess-Zumino term in their fermionic sector. We
demonstrate how the kappa-gauge symmetry appears in the purely supertwistorial
formulation and reduces by half the fermionic degrees of freedom of the two
supertwistors; a formulation of the model in terms of kappa-invariant degrees
of freedom is also obtained. We show that the kappa-invariant supertwistor
coordinates can be obtained by dimensional (D=6 -> D=4) reduction from a D=6
supertwistor. We derive as well by 6 -> 4 reduction the N=2, D=4 massive
superparticle model with Wess-Zumino term introduced in 1982. Finally, we
comment on general superparticle models constructed with more than two
supertwistors.
