If you want to focus on things over the past 5 or 10 years, that's fine. But digging up a paper from graduate school (essentially) is not a good argument at all. Focus on work he has done (started and completed) on his own after he left the nest.
What should the statute of limitations on research fraud be? Should it matter that Imai's work in the past 5-10 years continues to cite his 2005 APSR without qualification?