  We present the results of extensive simulations regarding the critical
behavior at the endpoint of the Roberge-Weiss transition for N_f = 2 QCD. We
confirm early evidence, presented in arXiv:0909.0254, according to which the
Roberge-Weiss endpoint is first order in the limit of large or small quark
masses, and second order for intermediate masses. A systematic study of the
transition strength as a function of the quark mass in the first order regions,
permits us to estimate the tricritical values of the quark mass separating the
second order region from the first order ones.
