Mindy...Great question! You will never be able to calm the nerves of tenants when it comes to crime. Their concerns may be well founded...for them. For someone else it may not even register. The "reasonableness" factor is not about appeasing your tenants as much as it is about your legal duty.
The bottom line is that you are actively pursuing a crime prevention "program". Lighting, maintenance, visibility, trash, and the other simple and low cost measures that help prevent crime. Don't jump over the practical solutions and go to security guards as a first step. If a murder occurs, then a guard patrol MAY be the immediate solution. That is a decision that is made with your legal partners. Your tenants may be unreasonable wanting a guard by their apartment but again, that is something you just have to work through.
Property owners do not have endless financial resources to provide "protection" to residents. No property owner offers protection for their tenants and visitors. Your residents should be able to vent (as I am sure they do on everything) but ultimately the decisions are yours as to what is reasonable. There are too many variables involved so your best resource is the crime prevention unit of the police department. If they have a Crime Free Multi Housing section contact them directly.
This link
taa.org/member/edufoundation/crimeawareness
will take you to a page where you can download the Texas Apartment Associate Crime Awareness Guide. The download link is under the last paragraph. This is an excellent tool for guidance on many things and it may give you some ideas for your own crime prevention planning.