BALTIMORE — Prosecutors want a specific police officer to go on trial first in the Freddie Gray case because they say the officer will be called as a witness to testify against two other members of the force, according to a letter sent to the judge.

Gray died after suffering a critical spinal injury while in police custody and six officers have been charged in his arrest and death.

Chief Deputy State’s Attorney Michael Schatzow asked Judge Barry Williams on Tuesday to schedule Officer William Porter’s trial first because he is “a necessary and material witness in the cases against” Officer Caesar Goodson and Sgt. Alicia White.

Porter, Goodson and White all face manslaughter, misconduct in office, assault and reckless endangerment charges. Goodson also faces a charge of “depraved-heart” murder.

Lt. Brian Rice and officers Edward Nero and Garrett Miller also face charges stemming from Gray’s death April 19. The officers will each be tried separately.

Gray, a 25-year-old black man, was arrested on April 12 after he ran from police in West Baltimore. Officers and their attorneys maintain he had an illegal switchblade, but prosecutors say Gray was in possession of a legal knife.

While handcuffed and shackled in the police transport van, Gray suffered a spinal injury. He died in the hospital a week later.

Porter was not present during Gray’s arrest, but met the police van at one of several stops it made before delivering Gray to the Western District station house roughly 45 minutes after he was detained.

Prosecutors say Gray told Porter that he couldn’t breathe asked for medical attention, but instead of calling a medic, Porter helped Gray off the floor and onto the bench, and did not secure him with a seatbelt, a violation of department policy.

Porter then followed the van to another stop, where prosecutors say Porter, along with Goodson and White, opened the van again to observe Gray, but this time the man was unresponsive.