People in jail or prison may discover that a warrant for their arrest is outstanding from another county, state, or the federal government. For example, someone in custody awaiting trial may be charged in another case in another county; or an inmate in a state prison may find that he is being charged with a another crime in a neighboring state.
In either situation, the issuing jurisdiction (the court that issued the warrant) may demand that the prisoner be brought before it to answer to the warrant. Usually, the defendant is transported to the court, enters a plea, and is returned to the original jail or prison, either right away or after additional proceedings. The original jail or prison and the issuing jurisdiction work out the details of where the prisoner will stay pending resolution of the case.
Prisoners who are the subject of an arrest warrant should contact an attorney as soon as possible. This is especially true for people who are awaiting trial or are about to enter a plea—often, a "deal" can be worked out with the jurisdiction that issued the warrant (assuming, of course, that the prisoner wishes to plead to the charge). For example, suppose someone is in jail on a burglary charge in Los Angeles County, and discovers that a neighboring county, San Bernardino, has also issued a warrant for his arrest. The defendant intends to enter a guilty plea in the LA case, and would do the same in the other case. The defense attorney and prosecutors in each county may work out a deal in which the defendant pleads to the LA case and the San Bernardino case; or pleads to the LA case in exchange for the dismissal of the other charge. The incentive for the prosecutors is that such a deal clears the case from the San Bernardino and LA courts, which are overloaded with cases; in exchange, the defendant receives a sentence that is less than he might have received had he allowed the second case to proceed independently.
Outstanding warrants for prisoners who are in state prison present a different challenge. Assuming the prison officials know of them but the issuing jurisdiction has not acted on them, they will block a prisoner's freedom at the end of his sentence. That is, when the prisoner has served his sentence, he won't be released—instead, a "hold" will be placed on him, and he'll be taken to the jurisdiction that issued the warrant.
Problems can arise even before the prisoner's release date. Outstanding warrants that are known to prison officials may interfere with the inmate's ability to take advantage of certain prison programs and privileges. For example, work release programs, benefits for good behavior, and even parole may be out of reach. An inmate may want to clear these warrants in order to avoid these consequences (but see the section below for situations in which clearing a warrant may not be a wise idea).
An attorney may be able to help the prisoner clear the warrant. Here are the steps that are usually followed:
Of course, these steps assume that the prisoner is willing to plead (or is fairly certain that the issuing jurisdiction will drop the charges once it learns that the defendant is already in state prison, particularly if the sentence is a long one). Prisoners who intend to fight the charge may want to do so while they also serve their original sentence; in that case, their demand letter will result in the case moving forward, and they may find themselves in the local county jail awaiting trial. If there's a conviction, the sentence can be tacked on to the prisoner's original sentence (a "consecutive sentence"), or it may be ordered to run at the same time (a "concurrent sentence"). An acquittal will mean that the prisoner will be returned to the prison to finish serving the original sentence.
However, in some situations, it may be to the inmate's advantage to leave the warrant alone and hope that the issuing prosecutors don't act on it. For example, suppose the warrant concerns an incident for which there is only one witness, who is elderly or seriously ill, or who is likely to move and become hard to locate. The inmate may choose to ignore the warrant, hoping that it will come to light, if at all, only at the end of the prisoner's sentence. By that time, the prosecution's ability to prosecute the case may be seriously compromised by the absence of the witness, who may have died or become impossible to locate.
As you can see, many tactical and practical considerations go into a decision on whether to bring a warrant to light and attempt to clear it or otherwise deal with it. Prisoners and non-lawyers are usually not in a position to know how the issuing jurisdiction is likely to respond to a demand for a speedy trial, nor are they likely to know how to bargain with the prosecuting attorney and reach a favorable plea deal. Only a local and experienced criminal defense attorney will know how and with whom to begin negotiations; and only a professional can advise you on the wisdom of letting a warrant slumber.