Nelson v. Tompkins

Jail's intake officer had fair warning that it was unconstitutional not to prevent the placement of a white detainee alone with cellmate who had stabbed a stranger solely for being white two days before; officer not entitled to qualified immunity from § 1983  action alleging violation of due process based on officer's alleged failure to protect detainee from being killed by cellmate; clearly established that prison officials had duty to take reasonable action to protect prisoners from violence at the hands of other prisoners, and also clearly established that officer violated duty if he knew of risk of substantial harm that one prisoner posed to another but failed to take any reasonable action to separate them.