Children, or rather "young adults", students, the age 15 or so. I am not sure that I know how their minds work nowadays. Back in time when yours truly were their age - we never threatened our teachers verbally or in writing. Certainly not threatened someone to their life. At least not where I grew up.
A very good friend of mine is in this horrid situation now.
My friend is a teacher. Not born in any of the Scandinavian countries. The prettiest little thing you'd ever see; petit with black hair. As sweet and friendly as can be. You name it. Now some of her students have threatened to kill her. Just because she didn't give one of them a passing grade. This person obviously didn't deserve to pass. It's not that she would randomly pass grades hither and thither. That's not how it is done here. But. Nevertheless. She was threatened to her life. What amazes me is that she had to ask the principal that these persons didn't come to her class anymore. Duh!! Would think they were sent home. Period. But no, that is not how it's done here.
In this country today a teacher can't tell a student who is misbehaving in class to leave the classroom. Read that again and ponder this! The student can misbehave: for instance talk on the cell phone, whistle, talk to his/her buddies and generally make an ass of him-/herself etc etc - but the teacher is still not allowed to make him/her leave the classroom.
I'm glad that I'm old(-ish) and don't have to go to school anymore! And I'm thankful for not being a teacher....