St. Thomas never gave a free will theodicy. Freedom is absence of compulsion, and absence of compulsion in the will does not explain how evil is even possible, much less how it could happen in fact. as far as STA was concerned, given that most of the universe was composed of the blessed angels and the saints, most of the universe was composed of beings that experienced no compulsion in their wills and yet could never commit a moral offence.
Evil has to be explained by imperfection: concretely, it happens because we can know things that we do not think about; more generally it happens because of a unique state of men in history and in via. God makes beings that can know things they don’t think about by making intellects with potency – and this was usually explained by his desire to create a universe with every grade of perfection. The broader historical predicament – unknowable except by revelation – was because of desire to glorify both man and himself in the Incarnation.