If a plaintiff waited to bring a lawsuit for several years, and in those years witnesses died and evidence was lost or destroyed, one equitable defense that the defendant may have is called:

The answer to this question is: Laches
Leaches refers to the unreasonable delay that people made before making the claim. In most cases, this type of things will resulted in dismissal of the case because the court see the case as irrelevant.
Depending on the states, you have the time limit of 5 - 10 years to report a criminal behavior.