I discussed this question a couple of years ago:
There is a notion that responsibility can be "shared", which I think is fundamentally misleading. We each make our decisions in an environment that has been made mainly by other people, but to judge any decision, legally or morally, we have to take that environment as given. Many people might have responsibility for any bad outcome, but they have it separately, they do not share it. We might put ourselves at risk of all sorts of dangers, from other people or from other elements of our environment, and if we are wise we will consider our own responsibility as we do so, but if we are the victim of a criminal, his responsibility is not lessened by our risky behaviour.
In the examples Copperfield gives, there are two general categories of responsibility that some victims have: Either they can fail to take ordinary precautions to avoid or prevent crime (failing to lock doors, leaving property unattended in a public place), or else they can deliberately involve themselves in illegal activity (buying goods that are probably stolen, dealing drugs, responding to 419 communications which are generally invitations to share in a theft or fraud).
My answer to his question is that the responsibility, if any, of the victim should not be a primary consideration for him. The reason is that he is not working on behalf of the victim. He is working on behalf of us all, as we all benefit from the rule of law. His job is not to undo the effects of the crime, which in most cases is impossible, but to bring offenders to justice in order to uphold the rule of law.
So what should be important for him is not the status of the victim, but the status of the offender. It might be the case that a thief who grabs a handbag from a pub table is a lesser offender, and a lower priority, than a thief who breaks into a car. I do not think that a mugger who hangs around in a "bad part of town" is a lower priority than one on the high street. Is a drug dealer who shoots other drug dealers a lower priority than a drug dealer who shoots passers-by? Possibly, but it is very marginal.