I imagine even if the person doesn't know the specifics of the case, they can take a look at the police report and make a professional assessment on whether it was a random attack or something else. It's also possible the phrasing resulted in a miscommunication between the "intelligence professional" and the person upthread (they could have said something like "it wasn't random", and Bob's grieving friend referred to that as a hit)

In almost every random stabbing, the person doing it is arrested, no? To be clear, I'm talking about random, unplanned, and unmotivated stabbings, not premeditated robberies and other similar crimes.