In other words, gun laws do little to nothing to prevent criminals from getting guns, but gun laws do prevent law-abiding citizens from getting them. To use your analogy, gun laws eliminate the sheepdog, not the wolf.You're right but there is a logical explanation. Criminals, being what they are, will be armed in both jurisdictions. In Virginia, they face an armed populace and are deterred, but in DC they are presented with a soft target rich environment by way of gun restrictions.
wolf + sheep = fed wolves
wolf + sheepdog + sheep = starving wolves
Guns are durable goods so proximity to supply is much less important than it would be for consumables but a large percentage of the guns used in crimes in DC come from next door in Maryland.