I am trying to prove structure theorems for Siegel modular forms by geometric means. This was successful for Igusa's subgroups \Gamma_2[2,4] as presented

Recently, Freitag and Salvati Manni used very similiar geometric approaches in order to prove a bit weaker results

They could even verify the results from my PhD thesis by modifying further the method

Together, the three of us could work out a common generealization of our results

More detailed informations on these publicatins can be found here.