Not necessarily. Police and other law enforcement agents (such as the DEA or FBI) don't have the power or authority to make binding plea agreements. Only a prosecutor can make a binding promise that you'll not be charged with a crime or that you'll receive a lighter sentence if you cooperate, confess, or agree to plead to lesser charges.
Police can tell you that they'll make your cooperation known to the prosecutor. They can tell you they'll recommend to the prosecutor that you receive a more lenient sentence or that all or some charges not be filed against you. But they can't make promises that are binding on a judge or a prosecutor.
If the police have made you such a promise, talk to an attorney about making sure the prosecutor will honor the promise.
Tags: police law enforcement agreements sentence cooperation prosecutor charges