I'm an idiot on anything as complex as these horrible shootings but this list shows a lot of anti-depressant use by the shooters. http://ssristories.com/index.php?p=school
I have no idea if it's credible or not but it seems to make sense when you consider the rate of these prescriptions in the US compared to the ROW.
Also, if anti-depressants contribute, I doubt they are the only cause. I bet Gun video games and movies are more heavily consumed and we know guns are more readily available, that has to increase the odds compared to other cultures.
How many of the parents are horrible people that should not be responsible for the development of a person?