Tony Hadlock, age 13, of Jamestown, N.Y., for his question:

WHAT IS AN EX POST FACTO LAW?

In criminal law, an ex post facto law is one that was enacted or decreed after an acs has been committed that may be illegal as a result of the new law but was not illegal at the time it was committed.

Ex post facto laws may also retroactively increase the punishment of previously committed crimes.

Article 1, Section 9 of the U.S. Constitution forbids all ex post facto laws. A law is not deemed ex post facto and hence unenforceable, however, if it affects only a retrospective change in the procedure whereby crimes are prosecuted.

Thus, laws allowing the prosecutor to introduce evidence that formerly had been excluded in criminal cases are not considered ex post facto even though these laws may have been enacted after the commission of the crime.