PHOENIX (AP) — Four legal-advocacy groups have asked the judge in former Sheriff Joe Arpaio's criminal case to appoint a lawyer to appeal the judge's decision to let the lawman's pardon stand.

The groups say in a filing Monday that a private attorney must be appointed to protect the independence of the courts.

The groups previously made unsuccessful attempts to get the pardon declared invalid.

U.S. District Judge Susan Bolton found Arpaio guilty of disobeying a court order in an immigration case.

She later declared the pardon valid and dismissed the case.

Arpaio attorney Jack Wilenchik says the groups have no right to make the request.

Daniel Kobil, a professor Capital University Law School who studies pardons, says he doubts Bolton would grant the latest request.