  The discovery of two active black holes in the Seyfert galaxy NGC 3393,
separated by about 490 light years, revealed a merging event. This led us to
look for other evidences of galaxy collision and merging through the analysis
of the observed spectra in different frequency ranges. We found preshock
densities higher by a factor of about 10 in the NGC 3393 NLR than in other AGN
and patches of ionized matter beyond the observed NLR bulk. They can be
explained by compression and heating of the gas downstream of shock waves
created by collision. Metallicity in terms of the O/H relative abundance, is
about 0.78 solar. Mg/H depletion by a factor of about 3 compared with solar
cannot be explained by Mg trapping into dust grains, due to rather high shock
velocities. The low O/H and Mg/H abundances indicate mixing with external
matter during collision. Twice solar N/H is predicted by modelling the spectra
of high shock velocity clouds reached by a Ts =8.6 10^4 K black-body flux. This
suggests that Wolf-Rayet stars could be created by galaxy collision in the
central region.
