one presumes it was an evolving system as the german govovovith. what's your feeling? >> of course, security screening is needed, but we should also bear in mind that the stage, the different levels of radicalization are not necessarily happening outside germany. the idea that such, that people that have terrorist attacks in mind planned this ahead before they entered germany. i think this is very often a misconception. we so he that, first of all, organizations like the islamic state doesn't need foreign nationals or migrants because there are many people with german, french passports -- anchor: it could have been spontaneous? >> not necessarily spontaneous, but it can be recent. we have seen that there have e state, the so-called, to radicalize people to reach out for people. anchor: thank you so much. it's dutiful to point out that it has not yet proven to be a terror attack. this is d.w. angela merkel wasn't the only person to visit today. the square has been turned into a makeshift memorial to the victims of yesterday's mass killing. >> a steady stream of mourners