California Code, Penal Code - PEN § 1127a

(a) As used in this section, an “in-custody informant” means a person, other than a codefendant, percipient witness, accomplice, or coconspirator whose testimony is based upon statements made by the defendant while both the defendant and the informant are held within a correctional institution.

(b) In any criminal trial or proceeding in which an in-custody informant testifies as a witness, upon the request of a party, the court shall instruct the jury as follows:

“The testimony of an in-custody informant should be viewed with caution and close scrutiny. In evaluating such testimony, you should consider the extent to which it may have been influenced by the receipt of, or expectation of, any benefits from the party calling that witness. This does not mean that you may arbitrarily disregard such testimony, but you should give it the weight to which you find it to be entitled in the light of all the evidence in the case.”

(c) When the prosecution calls an in-custody informant as a witness in any criminal trial, contemporaneous with the calling of that witness, the prosecution shall file with the court a written statement setting out any and all consideration promised to, or received by, the in-custody informant.

The statement filed with the court shall not expand or limit the defendant's right to discover information that is otherwise provided by law. The statement shall be provided to the defendant or the defendant's attorney prior to trial and the information contained in the statement shall be subject to rules of evidence.

(d) For purposes of subdivision (c), “consideration” means any plea bargain, bail consideration, reduction or modification of sentence, or any other leniency, benefit, immunity, financial assistance, reward, or amelioration of current or future conditions of incarceration in return for, or in connection with, the informant's testimony in the criminal proceeding in which the prosecutor intends to call him or her as a witness.