I am from France too.
As long as the authorities of USA do not put under control the possession of firearms, these tragedies will continue to happen again and again..
I have read 112.6 guns per 100 residents in the USA, that is where the problems comes from, guns are just to easy to get hold of. The next country on the list is Serbia, 75.6 per 100 residents. If guns are that easy to get hold of people will kill each other. Of course, a flat out ban on guns will never work but a concerted effort to halve the amount of guns in the country will and then control the sale of them better. For example, extend the ban on automatic weapons to all assault rifles and increase the price of ammunition.
There needs to be better response from the media too, stop showing pictures and giving the names of the shooters.
We do not feel safer when we have easier access to firearms.
I am from France and I absolutely disagree with Trump's position on this terrible attack. He says it's not a gun problem, but like many others, I think it is. Shooters may have psychological disorders, but if they didn't have such an easy access to firearms, it wouldn't be so simple to end the lives of so much teenagers.
There's definitely urgent decisions to take, as long as nothing is done, tragedies like that will continue to happen...