One who is required by law to take or who voluntarily takes the custody of another under circumstances such as to deprive the other of his normal power of self-protection or to subject him to association with persons likely to harm him, is under a duty to exercise reasonable care so to control the conduct of third persons as to prevent them from intentionally harming the other or so conducting themselves as to create an unreasonable risk of harm to him, if the [state] actor
(a) knows or has reason to know that he has the ability to control the conduct of the third persons, and
(b) knows or should know of the necessity and opportunity for exercising such control.
Butler ex rel. Biller v. Bayer, 168 P.3d 1055, 1063 (2007).
In cases of intentional attack, prison officials have a specific duty to protect an inmate from attack only when the attack is foreseeable. Butler ex rel. Biller v. Bayer, 168 P.3d 1055, 1063 (2007).