In order for his probation to be transferred to Georgia, Georgia has to agree to supervise him (they can refuse). His case remains in Texas but his probation is supervised there. There is paperwork that has to be submitted from the Harris County probation office to GA under Interstate Compact. See if you can speak with a supervisor about the procedure for expediting the request. An attorney may be able to help by asking the judge for permission to allow the move so the paperwork can be done, but we won't be able to do much. Our role in this is pretty limited; this is the purview of supervising officers.
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No, that will not be enough, however it will show the efforts he is making. He can call the court clerk to see what he would need to do to go in front of the Judge to see about getting transferred or speak to the PO superior to see if that gets him anywhere. An attorney would be more helpful, however you would simply have to call around to check prices or use the find a lawyer tab to contact some local attorneys. Hope that's helpful.
If Harris County approves the transfer request, Georgia still has the final say on whether he can move there. And unless it qualifies as an emergency transfer, he'll have to stay in Harris County until Georgia makes their decision.