School shootings - what is that?

In this text I'm going to write about school shootings:
A school shooting is, when a person or more go in to a school and kill pupils or teachers with a gun. Maybe it's because, the persons have had a bad childhood in the school, or they want to get revenge on the teachers.
A school shooter does often kill himself after the whole situation. Maybe he/she suddenly wakes up and sees, that it's a really bad thing, he/she has done, or the person doesn't want to get through the whole judgeing and prisoning.
I have heard about a man in the USA, who was a school shooter, and I think he got shot in selfdefence, or he killed himself. I think, there is more school shooting in USA, because people can get a gun very easily.
My oppinion about school shooting is, that it is a really serious crime, because it affects many people, and I hope it won't happen here in Denmark or other places.