One reason would be that the shooter may have used the word “normie”
Urban dictionary:
normie
A person who does not have a mental illness such as bipolar disorder, schizophrenia, mood disorders, PTSD, depression or any similar mental disability. “Normie” is a reference to those who are a part of the mainstream culture; the 97% of the population who do not have a mental illness.
“That’s just /r9k/. Pepe is the character that /r9k/ identifies with, along with wojak. Normies, or normal people, are using pepe for their own pleasure and it’s ruining pepe. REEEEEEEEEEEEEE is just the normal /r9k/ autist’s way of reacting to unwanted stimuli.”
https://www.reddit.com/r/OutOfTheLoop/comments/2znwmj/what_is_pepe_normies_and_reeeeeeee/