A supervisor is liable for constitutional violations of his subordinates only if the supervisor participated in or directed the violations, or knew of the violations and with deliberate indifference failed to act to prevent them. Wilson v. Seiter, 501 U.S. 294, 303, 115 L. Ed. 2d 271, 111 S. Ct. 2321 (1991); Taylor, 880 F.2d at 1045; See also Haynesworth v. Miller, 261 U.S. App. D.C. 66, 820 F.2d 1245, 1261 (D.C. Cir. 1987) (A supervisor who remains passive in the face of past constitutional violations about which he knew or should have known may be liable under 1983.). Federal courts have thus recognized a cause of action under 1983 when a plaintiff alleged that a supervisor's failure to train or to supervise personnel led to the deprivation of constitutional rights, or when a policy existed that led to the deprivation of such rights. Ybarra v. Reno Thunderbird Mobile Home Village, 723 F.2d 675, 680 (9th Cir. 1984).