Can I legally break a lease if I no longer feel safe in my apartment complex?

The ability to vacate a premises due to constructive eviction is well-settled in the State of Nevada.  Constructive eviction occurs when, through the actions or inaction of the landlord, the whole or a substantial part of the premises is rendered unfit for occupancy for the purpose for which it was leased. One such condition is the responsibility of a Landlord to provide adequate heating and air conditioning.  Failure of a landlord to perform the government-ordered alterations (such as by the Health Department or Building Department) can constitute constructive eviction. The key aspect of constructive eviction is that there must be a duty on the landlord to provide the element of the tenancy for which you are being deprived.  In the case you cite above, you would need to show that the Landlord had a duty to provide adequate security and has failed in that requirement.  Merely because the tenant no longer feels safe in the neighborhood or believes that adjoining properties contain a nuisance beyond the Landlord's control would most likely not rise to the level of a constructive eviction.