It would depend on the situation. Was there someone who was supposed to be acting as a caregiver and supposed to be with them? Cause that would change it. In that cause it would be both the attacker and the caregivers fault in my opinion. It would never be the elderly persons fault, they did not ask to be attack just because they went for a walk, no matter how late at night it is.
The Victim is just that the victim. They should not be to blame, because someone decided to attack them. The same would go for a girl who was attacked, because she was wearing tight clothing or a short skirt. Just because they dressed that way does not mean that they asked to be attacked. That was a decsion that was made once agian by the attacker. Sorry if I offend or ruffle feathers, but the victim in my opinion should not be blamed.