While landlords aren't necessarily responsible for the actions of their tenants, they should take basic steps towards crime deterrence. It is up to you to keep a general eye on your property and the activities that occur there.
What Can I Do to Prevent Crime at My Property?
Doors, Windows, and Locks
As a landlord, you are required to ensure that your property is physically secure. Your tenant should be able to easily lock the windows and door(s) in their unit. For extra security, you could consider adding a deadbolt to the door(s).
There are a lot of lighting options to help illuminate your property at night. Some examples include porch and backyard lights, floodlights (within reason -- not bright enough to annoy the neighbors!), and motion-activated lighting. Recommend that tenants set up a lamp or other light on a timer when they are away to deter potential criminals.
Blight attracts crime, so keep your property up to code. Buildings in poor condition (especially vacant ones) indicate that no one is paying attention to or caring for the property. These buildings are sometimes seen by criminals as ideal hiding places for drugs, weapons, or people.
Many types of security systems exist these days -- everything from home alarms to motion-activated video cameras to property monitoring services. If crime is an issue in the neighborhood surrounding your rental, it may be wise to invest in added security to protect your property and its residents. Your tenants, and their neighbors, will thank you for it.
Landlords are also responsible for screening their tenants. A prior criminal conviction does not necessarily indicate that someone will be a poor renter. Still, you have a responsibility to keep your tenants safe, and it may not be appropriate to allow people with certain prior convictions to move in (e.g. allowing a sex offender to move into one unit when there are children in the other).
Know the Signs
The following may constitute warning signs of criminal activity:
Having large quantities of cash on-hand
Wealth that is inconsistent with the person's occupation
People loitering around the property
Visitors at all hours and for short periods of time