A Reston reader has a question. He writes, "Your paper said the other day that the FBI had investigated a loan obtained by James Denson, chairman of the D.C. ethics board, and had concluded that Denson forged another man's signature on a deed of trust to obtain a $30,000 loan guaranteed by the U.S. government.

"The story went on to say the FBI dropped the investigation because 'the five-year statute of limitations had expired.'

"The date of the alleged forgery was 1972. It wasn't discovered until 1977, at which time the FBI was called in. The FBI's decision not to prosecute was made in 1978. Can you tell me whether the statute runs from the time of an alleged offense or from the time it is discovered? How can a victim prosecute before he knows he's been victimized?"

The United States Attorney's office explained the matter to me in such simple terms that I'm sure any lawyer would have understood exactly what was said.

Alas for me, I am not a lawyer.

However, I think I absorbed a few basics. The statute of limitations begins to run when a crime is committed, not when somebody discovers that the crime was committed.

The normal period during which charges can be brought is five years, but other terms are specified for other offenses, especially under state laws. There is no time limitation on prosecuting some crimes, e.g., murder.

Certain actions by the perpetrator of a crime can stop the statute from running. I think the examples given were, "If the criminal flees or tries to hide evidence of his crime."

In other words, one who forges a signature must hope that five years will elapse before anybody finds out what he did.

What's the rationale for giving a defendant such protection? "Witnesses die, or they move away and can't be found. Memories dim. Documents disappear. It's not fair to delay prosecution for so long that an innocent person can no longer present an effective defense."

P.S.: If this column should come to the attention of an offender who thinks he's home free because of something I wrote here, I suggest that he consult an attorney. I am not an authority on legal matters.