Hans-Jakob Schindler is senior director of the Counter Extremism Project, a non-profit that helps combat the threat from extremist ideologies. 

For hardened extremists and highly motivated terrorists, deradicalization programs are not very effective, Schindler tells DW. It's too early to say what exactly went wrong prior to the attack, but lessons have to be learned, he says. 

The expert explains what could have motivated the attacker, why the LGBTQ+ community is a target for extremists and why it is a challenge for German authorities to keep pace with terrorists.