The person you are replying to did not say guns caused the tragedy. Rather the availability of guns in the U.S. is why we see school shootings every week in the U.S. and not in Europe.
When people in other countries lose their minds they cannot go on rampages as easily because of filters on gun ownership.
In fact before people go on rampages they often go to the US first to get guns so their rampages can be more 'effective' where they actually do live:
They totally can, for instance: https://en.wikipedia.org/wiki/School_attacks_in_China:
> On March 23, 2010, Zheng Minsheng (郑民生)[7] 41, murdered eight children with a knife in an elementary school in Nanping,[8] Fujian province...
> An attacker named Wu Huanming (吴环明), 48, killed seven children and two adults and injured 11 other persons with a cleaver at a kindergarten in Hanzhong, Shaanxi on May 12, 2010...
> On 4 August 2010, 26-year-old Fang Jiantang (方建堂) slashed more than 20 children and staff with a 60 cm knife, killing three children and a teacher at a kindergarten in Zibo, Shandong province....
> The death toll has risen to nine in Friday's stabbing attack outside a middle school in northwestern China allegedly carried out by a former pupil seeking revenge for having been bullied....
etc.
> Reaction and response
> ...The state media has also been keeping news of these attacks quiet by deleting forum entries on the internet and releasing few facts on the incident for fear of copycat crimes and mass panic...
> Following the Chenpeng school attack, the Chinese government began posting security guards in schools throughout the country. It was planned that all schools have a security guard by 2013.
There's a reason 99.8% of this stuff is done with guns. AR-15s, to be specific, or something very similar.
It's because that's what is easy. These people aren't geniuses.
If you take the assault weapons away, the vast majority of this will just stop happening. This is a solved issue. We know how to solve it.