It's meant to obscure the crimes that were happening.
I no more know what the author's intent was than you do, but I'm going to go with a more charitable interpretation: it's meant to clarify the means by which the robbery took place. In other words, the exact opposite of "obscure". But if you have a narrative, by all means stick to it.
Let me reverse what you said: "Rob" sounds more threatening. And, in fact, it is more threatening - I lose my money either way, but "rob" means I'm more likely to also be injured or killed.
