Are there similar psychological traits between the killers?
- Yes, depression and social problems

Were there school shootings prior to video games?
- Yes, wikipedia lists three shootings as early as the 70'ies.

Are there school shootings in all nations in which violent videogames are popular?
- No, the vast majority happens in the states. Videogames are very popular in places like Sweden that do not have any school shootings up to date but the psychological traits exist in other nations than the states

Can videogaming be linked to such profiles?
- No, videogames do not lead to depression. Like with "videogame addiction" it's easy to draw a correlation between excess use of games and the psychological state of the person, but this also lead to a false causation. It's not that people try to escape to play videogames, but that people play videogames in an attempt to escape.