BALTIMORE, Md. (WUSA9) -- Maryland’s highest court heard arguments about whether one of the police officers charged in the Freddie Gray case can be forced to testify against his fellow officers Thursday.

The outcome could make or break the prosecution's cases.

Officer William Porter said a promise of immunity in exchange for his testimony in Maryland would be worthless if the case is taken up in federal court.

The situation is complicated by the fact there was a hung jury in Porter’s trail – and he faces a retrial.

The cases against the other officers in the Freddie Gray case are on hold until the Maryland Court of Special Appeals decides what to do.

Thursday's hearing was the first time all six officers charged in Gray's death were all in the same courtroom.