If the accused is afraid of unfair treatment, like Julian Assange after the treatment of Bradley Manning, then it would be reasonable for them to want to stay a

If the accused is afraid of unfair treatment, like Julian Assange after the treatment of Bradley Manning, then it would be reasonable for them to want to stay away from that country until they received certain assurances or have the charges dropped (Gary McKinnon is another case to think about). If you set the process going then trying them in their absence would be convenient for the state but not fair to them.