The judge overseeing the trial of a man accused of killing a Donna High School student in 2020 will rule on a motion to call for a mistrial.

Carlos Julian Contreras, 23, was arrested in connection with the death of 18-year-old Genaro Isaiah “Izzy” Castillo on Jan. 12, 2020.

The defense is calling for a mistrial after they claimed prosecutors offered immunity to a witness without letting the defense know.

The Hidalgo County Sheriff's Office at the time said Castillo's body was found near Donna Lake by a field worker along Valley View Road.

According to a criminal complaint obtained by Channel 5 News, Castillo’s body was found with gunshot wounds, and .40 caliber bullet casings were found near his body.

After interviewing Castillo’s family, investigators learned he was friends with Contreras. A bloody napkin was found inside Contreras’ vehicle, and .40 caliber bullet casings were found in the bed of his truck, the complaint stated. 

During a news conference following Contrera’s arrest, Hidalgo County Sheriff Eddie Guerra said Contreras admitted to picking up Castillo and driving him and another man identified as “Jorge” to the area south of Donna Lake. Contreras claimed "Jorge" was the one who fatally shot Castillo, but the sheriff said investigators don’t believe a “Jorge” exists.

Through the investigation, authorities learned Castillo and Contreras were arguing over money linked to criminal activity when the shooting happened.

Contreras’ trial was supposed to start on Monday. Instead, his defense team filed a motion for mistrial after learning that prosecutors offered “full immunity” to a “central witness.”

According to the defense, the witness was offered immunity days before jurors were selected, calling into question whether jurors “could evaluate the testimony of a witness testifying under immunity.”

“By failing to disclose this arrangement, the state allowed the jury to be selected under false pretenses. Jurors were invited to excuse credibility defects as ordinary human behavior, when in fact those defects were tied to a material impeachment issue—an undisclosed immunity agreement—that went to the core of [the witness’ bias and motivation,]” the motion states.

A hearing was held on Wednesday where the judge said a decision would be made on the motion.

A new hearing date was not set as of Wednesday evening.