18 U.S.C. 3282
"...no person shall be prosecuted, tried, or punished for any offense, not capital, unless the indictment is found or the information is instituted within five years next after such offense shall have been committed." This means that the Federal Government must file an information, or seek an indictment, within 5 years.
When did the Crime Occur?
Determine when the most recent "crime" occurred, or is alleged to have occurred, and count forward five years. That is the date on which the government loses the right to prosecute for the crime. There are a few exceptions to this general rule, but in essence, if you have passed the five year deadline without being formally charged with the crime, then you are "in the clear".
EXCEPTION: Capital Offenses
"An indictment for any offense punishable by death may be found at any time without limitation. " 18 U.S.C. 3281 If the crime alleged is punishable by the death penalty, then there is no limitation on when the prosecution can begin.