Ok, the reason I ask is because certain criminal actions cannot be prosecuted after a certain time. This is called the Statute of Limitations. Because this is a crime involving Fraud, the Statute of Limitations is 4 years from when the fraudulent activity occurred, or 4 years from when it was first discovered, whichever is later.
Because these actions have occurred within the past 4 years, you do not need to worry about the Statute of Limitations.
Because the allegations constitute a state criminal offense, the state has the authority and jurisdiction to investigate and file any charges that need to be brought as a result. Specifically, it will be the local police department where the fraud occurred (so for instance, if the fraud occurred in Town or City X, Town or City X Police Department would be the proper authority to report the criminal activity).
It is as simple as contacting the police department (or calling them) and asking to file a police report for the activity. The police will then speak to you in-depth about the activity (when it occurred, who committed it, how it occurred, how you found out about it, etc). After that, if the police think a crime has been committed, they will attempt to speak to the individual suspected of the offense. They will also attempt to obtain any document that may have been forged through the legal subpoena process and further inquire into those documents.
If, after the conclusion of their investigation, the police department think a criminal action occurred, they will refer the matter to the local District Attorney's Office. The DA's Office will then look into the matter as well and, should they reach the conclusion that there is probable cause that this person committed forgery (or any related offense), they will file charges or seek charges from a Grand Jury. This will then begin the criminal prosecution process.