IF the landlord knew of the problem, had a reasonable opportunity to fix it after being made aware of it, and, despite that knowledge and that opportunity, failed or refused to fix it, then they may be liable; in that case, they would have been negligent, or unreasonably careless, and violated their duty to provide reasonably safe premises for rent.But knowledge and opportunity to repair are critical. If you can't show that they knew of the problem (e.g. you never reported it) and/or if the robbery occured very shortly after you reported  it (since landlords must be given a chance to get a contractor or repair person in), then they did nothing wrong and would not  be liable.