Karl Pierson, the 18-year-old who opened fire on a high school in Colorado "held strong political beliefs" according to his classmates.
After opening fire at Denver's Arapahoe High School in what the local county sheriff said was most likely a "revenge attack" on a teacher, the teenager fatally shot himself.
A 15-year-old girl was seriously injured in the attack, and two other students were wounded, but have since been released from hospital.
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Doug Bergeson, from Wisconsin, USA, calmly drove himself to hospital and walked into the emergency room to ask for help.
The venue will open its doors again for the first time since May's bombing on September 9 for the We Are Manchester concert .
Reports peaked in June, when the London Bridge and Finsbury Park attacks took place, with the service receiving 5,703 calls.