The concepts developed for direct photo-double ionization are deployed to a
nalyse recent experimental data for indirect or resonant photo-double ioniz
ation of Ca in the region of the 3p-3d resonance given by Ross et nl. As in
the direct process the features in the triple differential cross sections
can be understood in terms of selection rules, final-state electron correla
tion and interference effects. For most directions of the two-electron mome
nta strong destructive interference between various partial waves is found.