One of six Baltimore police officers charged in the death of Freddie Gray is asking a judge to quash a subpoena for his testimony in the upcoming trial of a fellow officer.

William Porter's attorneys filed the motion on Monday saying that he plans to invoke his Fifth Amendment protections against self-incrimination and decline to testify in the trials of Caesar Goodson and Sgt. Alicia White.

Porter was the first of the officers to be tried, last month. Jurors could not reach a verdict, however, and a judge declared a mistrial. Porter's retrial has been scheduled for June 13.

Gray died in April from injuries that prosecutors say he received while riding in a police van following his arrest. Goodson was driving the van.

Goodson, Porter and White all face manslaughter, assault, misconduct in office and reckless endangerment charges. Goodson faces an additional charge of second degree "depraved-heart" murder. Gray's death led to protests and unrest that resulted in millions of dollars in damages.

Porter testified during his own trial last month. The state had previously indicated that prosecutors planned to call him as a witness against Goodson and White. But because of the mistrial, Porter has a Fifth Amendment right not to incriminate himself on the stand before his case is complete. Still, prosecutors issued subpoenas last month seeking his testimony.

Porter's attorneys argued in their motion that forcing him to testify would "effectively render the Fifth Amendment meaningless."

His attorneys also argued that if Porter were to take the stand prior to his own trial, no matter the outcome, his credibility would be adversely affected.

"If Officer Goodson or Sergeant White were to be acquitted it is all but inevitable that jurors would conclude that Porter — the star witness — was not credible," the filing reads. "If convicted, the jurors will assume that Officer Porter has knowledge of inculpatory acts that he has now revealed when granted immunity."

Prosecutors and defense attorneys are barred by a gag order from commenting on the case.