Having him deported would be a disaster for Marion's case.
Plus having him in prison for other offences would make it much harder to get access to him, especially with the case becoming more well known and maybe he might lawyer up with some pro bono lawyer wanting to make a name for themselves.
Also, I know some would maybe like it, but what happens if he gets attacked by other prisoners. It has been known to happen. He could die and that would be the end of getting any more information about Marion from him.