Some of the issues here are that many people treat other people with hearing (Or speaking) problems as dumb or worse. I have had many friends with this type of issue, including a co worker who grew up with both parents both deaf and speech impaired, Note the words used there. I have been in his house, and interacted with both of his parents, and could see clearly that they seemed pretty dumb. In reality, they both had graduated from Gallaudet College for the deaf. At work, his father was denied promotion, as his superiors were not willing to give him a complex job, he had to have all his instructions in writing. Their son, my friend, learned to talk interacting with the neighbor kids, and they were not consistently nice to him.
That being said, this deaf man was fitted with hearing aids, and immediately started hearing what people had been saying about him all the time. A well balanced person would have turned around and pointed out that such talk was offensive, and he could hear now.
Unfortunately, he had a lifetime of subtle abuse, and had little confidence in verbally responding to such comments. He checked in to the hospital, and it would seem that they did not succeed in teaching how to react to such abuse, in a positive way.
A double failure, but it must be pointed out that they could not refuse to allow him to check out, as he was otherwise a functioning citizen.
Soon after hearing the details of where he had done the killings, and that these had been his friends and fellow players in simple games, I predicted that after he stopped running, and thought of what he had done, he would kill himself. For better or worse, that is what happened.
From another perspective, I have a very good friend who lives near the site of the shootings, and his sister is close enough that she heard the gunfire. I had an internet conversation with him the evening after the shooting, while he and his sister were in lockdown.
I do not intend to justify what he did, but do understand that some who died were the cause of the whole catastrophe.