Don't underestimate street junkies on what they can or will do. Remember, they live on the street so they probably know more about what goes on in the neighborhood than you do. Things like who comes and goes and at what time and how. Just because they haven't done anything doesn't mean they don't have the capacity. Their existence is dependent on keeping their normalcy. If that gets threaten their complete system, particularly his need for her to be with him, will be something he may fight for. Its all about getting that next hit and I'm sure she has much more value in getting those resources than he does.