Full disclosure:

1. I am not a psychologist, psychology is merely a hobby.
2. I am from the US, but I will try to stick to my understanding of human emotions as a whole.

One thing I have observed about violence that seems random is that they are often performed by people who have been proverbially "beaten down" by life. When this is the cause, they may feel the need to lash out, but their "beating" was so severe that they become apathetic. They just need some outlet for their pain, rather than a specific individual or group.

Some people will take it out on themselves and it becomes self-harm or suicide. Others will take it out on those who are vulnerable in their immediate vicinity.

Basically, when a person is in a lot of pain, it becomes harder to think about others, because they are already struggling with their own issues. At least from where I stand, random acts of violence is what happens when that idea is taken to an extreme.

As for articles and videos: I'm not sure if you will be able to view the video on this page easily, but there is a transcription on the page: it was shared by a man who claimed he almost became a school shooter. He described what he was going through and feeling leading up to the moment where he almost did it. I think it provides a window into how suffering makes a person volatile:

https://www.ted.com/talks/aaron_stark_i_was_almost_a_school_shooter?subtitle=en

In a similar vein, depression tends to cause a person to focus heavily on their own thoughts and emotions and less on their social connections, not because the person is selfish, but as a means of self-preservation, as described in these articles:

https://neurolaunch.com/is-depression-selfish/

https://www.healthyplace.com/blogs/copingwithdepression/2020/12/when-depression-makes-you-appear-selfish

This is just one possible explanation, but it's the one I am most familiar with personally. I hope this helps.