The Perry phony case was trumped up by the Texas Public Integrity Unit, which is part of the office of the Travis County District Attorney (Travis County being the county in which the state capitol is located).
The TPIU seems only to indict Republicans. They also got Tom Delay.
This prosecution seems to be coming from a special prosecutor; I am not able to discover who hired the special prosecutor.
According to the The Texas Tribune special prosicutors were appointed by Collin County officials after Collin County District Attorney stepped aside.
From article at https://www.texastribune.org/2015/07/01/potential-case-against-paxton-appears-grow-serious/
“...were appointed earlier this year after Collin County District Attorney Greg Willis, a Paxton friend and business partner, stepped aside. Before that, Willis had asked the Texas Rangers to look in to the allegations against Paxton.
Paxton’s legal drama landed in Willis’ territory after Travis County prosecutors declined last year to pursue charges against Paxton, referring the allegations to Collin and Dallas counties. Dallas County District Attorney Susan Hawk passed on a case.”
It was state district judge Scott Becker. The Collin County prosecutor recused himself which bumped the case up to the district court judge who examines the merits of the complaint and if needed hires a prosecutor(s)
In spite of what you say, this is similar to what happened with Perry.
The complaint against Perry was filed with the Travis county prosecutor, who recused herself, bumped the case up to the district judge, who recused herself, bumped the case up to the appellate court judge Billy Ray Stubblefield(Perry appointee), who hired retired/visiting judge Bert Richardson to hear the case in the district court. Richardson hired McCrum as the prosecutor.