It appears that our prime minister believes it would be inappropriate to bring retrospective legislation in to charge David Hicks with offences in an Australian court, but does think it is OK for the USA to do so, even though some prominent US citizens don’t think too highly of ex post facto legislation:

“The sentiment that ex post facto laws are against natural right, is so strong in the United States, that few, if any, of the State constitutions have failed to proscribe them. The federal constitution indeed interdicts them in criminal cases only; but they are equally unjust in civil as in criminal cases, and the omission of a caution which would have been right, does not justify the doing what is wrong. Nor ought it to be presumed that the legislature meant to use a phrase in an unjustifiable sense, if by rules of construction it can be ever strained to what is just.”

(Thomas Jefferson, Letter to Isaac McPherson, August 13th, 1813)