Once the Wizengamot would vote Harry guilty, Albus’s plan was to get Harry thrown in prison—then later, to arrange for Harry to be granted a pardon; the boy would be pathetically grateful to his former headmaster for his "freedom." After several years of scanty prison food, and constant exposure to Dementors, Harry would be easy meat for Tom. Once Harry died, the prophecy would be fulfilled, then Albus could go in and remove Tom, in the process grabbing glory for the Greater Good.