Mental illness.
That's the common denominator. What normal person would kill another, especially children and innocent people.
Most people have never heard of the Bath School Incident that happened almost 100 years ago. And NO firearm was used! Yet 38 children killed, 6 adults and at least 58 injured.
People should get to the root cause...look for warning signs and nowadays social media. These people were all sick!
Here it is:
"The Bath School disaster, also known as the Bath School massacre, was a series of violent attacks perpetrated by Andrew Kehoe on May 18, 1927, in Bath Township, Michigan, United States. The attacks killed 38 elementary schoolchildren and 6 adults, and injured at least 58 other people. Prior to his timed explosives detonating at the Bath Consolidated School building, Kehoe had murdered his wife, Nellie Price Kehoe, and firebombed his farm. Arriving at the site of the school explosion, Kehoe died when he detonated explosives concealed in his truck."