730 ILCS 125/19.5
The sheriff may adopt and implement a written policy that provides for the release of a person who is in the custody of the sheriff for any criminal or supposed criminal matter to sworn law enforcement personnel or to the State's Attorney for the purpose of furthering investigations into criminal matters that are unrelated to the criminal matter for which the person is held in custody. The written policy must, at a minimum, require that there be a written request, signed by an authorized agent of the law enforcement agency or State's Attorney office, to take custody of the prisoner and that the written request shall include the name of the individual authorized to take custody of the prisoner, the purpose and scope of the criminal matter under investigation, and a statement of the fact that the individual taking custody and agency they are employed by understand the limitation of the sheriff's liability as described in this Act. Upon the release of a person to law enforcement personnel or the State's Attorney under written policy of the sheriff, the sheriff shall not be liable for any injury of any kind, including but not limited to death, to either the person released or to any third party that occurs during the time period that the person is in custody of other law enforcement personnel or the State's Attorney unless the sheriff or a deputy sheriff, correctional guard, lockup keeper, or county employee is guilty of willful and wanton conduct that proximately caused the injury.
730 ILCS 125/19.5