The Founders' Constitution
Volume 3, Article 1, Section 9, Clause 3, Document 9
http://press-pubs.uchicago.edu/founders/documents/a1_9_3s9.html
The University of Chicago Press
Article 1, Section 9, Clause 3
Document 9
Oliver Ellsworth, Landholder, no. 6
10 Dec. 1787
Essays 163
There is to be no ex post facto laws. This was moved by Mr. Gerry and supported by Mr. Mason, and is exceptional only as being unnecessary; for it ought not to be presumed that government will be so tyrannical, and opposed to the sense of all modern civilians, as to pass such laws: if they should, they would be void.
The Founders' Constitution
Volume 3, Article 1, Section 9, Clause 3, Document 9
http://press-pubs.uchicago.edu/founders/documents/a1_9_3s9.html
The University of Chicago Press
Ford, Paul Leicester, ed. Essays on the Constitution of the United States, Published during Its Discussion by the People, 1787--1788. Brooklyn: Historical Printing Club, 1892.