To greater or lesser degrees, we all try to predict behavior, LE included. For most of us, it's simply situational awareness. It's not so much a matter of "knowing what someone has in mind" as it is about knowing that behaviors X and Y are often followed by behavior Z. For example, in Terry v. Ohio, an experienced law enforcement officer testified that he had seen three men (I have to paraphrase here) go back and forth in front of a store several times with kind of a "practiced indifference," which the LEO interpreted as them casing the store for a robbery that they planned later.
A gunfight is not the time to learn new skills.
If you ever have a real need for more than a couple of magazines, your problem is not a shortage of magazines. It's a shortage of people on your side of the argument. -- Art Eatman