Your rights are determined via the lease you signed. I am sure there would be a disclaimer clause like the management is not responsible for theft, stolen property and vandalism. Even if they don't have the disclaimer, you probably have little rights to enforce anything here. Once they told you that no security is provided for the complex, that is all they needed to inform you. If I were you, I would take the rent reduction as I do not see any direct negligence of the apartment complex in this matter. Maybe you can ask other tenants and file a nuisance suit against the complex, but probably no financial outcome here.
Only see a licensed attorney before you make any decision. This answer may not be perfect in any given situation. However, more fact may be required by your local attorney. If you are in Las Vegas, you are welcome to send your questions regarding Chapter 7, or 13 to Attorney Malik Ahmad at Malik@lasvegaslawgroup.com or www.fastbankruptcynevada.com or by calling (702) 270-9100. In many cases, we do not charge initial consultation fee.