Also, I don't buy into the idea that it is always possible to tell who is capable of heinous acts of violence. Some people, yes, some are obvious.
Nobody said this.
JonLaw said it's "often" possible to tell who is "kind of prone" to doing crazy things. I wrote that I agreed about being able to spot people who need to be monitored or helped.
If people had been paying attention to the Columbine kids, their plans would have been obvious. Everything was detailed (well in advance) on paper, on video, and on a website. Multiple people failed in ordinary ways, and the result was disastrous.
IMO, there are systemic and social barriers that allow kids like the Columbine pair to slip through the cracks. This is why it's important to analyze everything leading up to these events and look for patterns, both in the perpetrators themselves and the responses to them in the years/months leading up to attacks. Did the shooters stockpile weapons? Did they create extremist writings? Were there diagnoses of mental illness or allegations thereof? Did people make credible complaints about the shooters? Did the cops take the complaints seriously (in the case the Columbine, the answers to the last two questions are yes and no.)? Etc. When we try to look for individual causes (they were goths, they were bullied, there were guns in the house, it was a reaction to meds, no one knew, etc.), we set ourselves up for another round of shootings.
These problems are complex, which is why it's important to find a way to identify not only the signs that might help identify someone who needs help, but also the signs that might identify when others are overlooking things they shouldn't.
