He's 17, a refugee from a war torn country, he travelled to Germany as an unaccompanied minor.
It's fairly safe to assume that he's been through trauma, he's separated from his family. I have sympathy for him. He's been let down by a lot of grown ups, foreign policies etc. Poor kid. He's dead now, it's a tragedy.
I also have a huge amount of sympathy for the four victims and their families (14 others treated for shock - I have sympathy for them too)
Compassion is very important. Without it the whole world would be constantly at war, charities wouldn't exist etc