A statute of limitations is a defined time period in which a legal action may be taken. The statute of limitations for different types of lawsuits usually begins with awareness of the harm or injury. The length of the statute of limitations depends on the type of case and the jurisdiction (usually the state) in which it is filed.
If a legal action is not filed within the prescribed time, it cannot be brought, even if the case would otherwise have merit.
In U.S. law there is no statute of limitations on murder.