Many of the negligent security cases castigate the property owner for failure to protect residents from criminals who are able to enter the premises. They ask the courts to demand that landlords provide security guards, locked gates, and special lighting. But none of these precautions against outsiders can prevent tenant-on-tenant crime.

If there is a duty on the part of the landlord to protect the tenant against criminal acts perpetrated by a fellow tenant, landlords of both residential and commercial properties may then be found to have a duty to investigate their tenants, both prospectively and continuously during the tenancy, to determine the tenant's propensity for criminal behavior. The landlord would have to decide whether to screen prospective tenants for criminal propensity, refuse to rent to such individuals, or evict tenants who are potentially dangerous to other tenants. If the landlord does take action to protect other tenants, the landlord may face claims from the dangerous tenant who has been subjected to the landlord's protective actions.

Predicting which tenants are likely to commit future crimes can be a complicated, if not impossible, task. It is difficult for landlords to find reliable crime predictors that do not invade the privacy of potential tenants or impermissibly discriminate against them. Public records often do not provide a complete story, nor are they necessarily easily and cheaply accessible. Assuming the landlord is liable for foreseeable criminal acts by one tenant against another for negligently renting to the offending tenant, does the landlord have a continuing duty to check the local police records for information regarding current tenants? Must the landlord regularly question other tenants or review criminal records during the tenant�s occupancy to determine whether the tenant had exhibited a criminal propensity that may not have existed at the time of first rental?

Tenants have privacy rights and protections based on personal characteristics, even if those characteristics may lead to violence. For example, statutes such as the Fair Housing Amendments Act protect the mentally ill, even those individuals who may show the potential for violence, from any adverse action based on discovery of the fact of the mental illness or violent propensity. State statutes usually provide similar or expanded protection. This is yet another reason why it is impractical and unwise to place landlords in the position of discerning their tenants' propensities for violence.