What is a non prosecution agreement?
The more correct phrase or term would be "immunity" or the government's "agreement not to prosecute." Generally, it is improper for a prosecutor to promise an accused, in return for a confession of guilt regarding a particular crime, immunity from prosecution for other crimes that he or she may have committed, but the state may contract with an accused for his or her exemption from prosecution in return for his or her honestly and fairly making a full disclosure of the crime on the trial of a confederate whether or not the confederate is convicted.
When agreements of this character have been made by the prosecuting officer with the consent of the court, as is usually the case, the court will see that the public faith which has thus been pledged is duly kept, although sometimes the courts have refused to enforce such agreements. The witness must keep his or her part of the contract strictly if he or she hopes to receive the promised immunity; if his or her testimony is corrupt or his or her disclosure is only partial, the witness gains nothing, but forfeits his or her right under the contract.
In determining the validity of agreements not to prosecute or of plea agreements, courts generally refer to the rules of contract law.