It is all in the mindset of what someone is thinking. Someone who is an accountant, thinks like an accountant. A manager will think like a manager. A CFO will think like a CFO. They all have a different form of thinking that has been molded over the years. Just like someone going into/in the criminal justice/investigative field, thinks like an investigator. You think outside the box. You find something suspicious, you want to investigate and see where it leads. You go to conferences, meetings, you attend training and take classes where you learn a skill set around investigation and what to look for when it comes to suspicious people.
There are common traits and common clothing that criminals where. Like what Malorn said above, one wearing a hoodie use it to conceal. Just like when your credit card company cancels your card because they see that in one day, you fill up a car twice and buy athletic shoes (for whatever reason, when someone takes your credit card, that is typically what they buy. A tank of gas for them and a friend and a pair of shoes). When it comes to statistics, criminals tend to share the same traits over and over again. It is best to know what those traits are and to avoid them...
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