Well, yes you do know. These are all subcategories, but it comes down to marginalization. School shootings are almost entirely young white men who have been marginalized by society as a whole. After every school shooting we talk about bullying, why? Because we know that has a major effect. Now, when a muslim shoots up people on the street or drives over them in a truck, it's not because of being marginalized by society, they couldn't care less about that. It's about Islam, plain and simple. We can talk about upbringing, political and western policy and mental illness all day long, but those ideas just lead to the real reason - Islam.
Not all muslims pull off these attacks, just as not all young men shoot up schools, but when an attack is described on the TV, one can guess the gender, race and age span of the killer before the news announces it. It's not rocket science.