Prosecutors in Baltimore are asking an appeals court to compel one city police officer to testify against another in the Freddie Gray case, after a judge refused to do so.

In a filing made public Friday, the Baltimore State's Attorney's Office says it's appealing Circuit Judge Barry Williams' Jan. 20 decision blocking prosecutors from calling William Porter as a witness against Edward Nero and two other officers.

Nero faces trial Feb. 22 on charges of second-degree assault, misconduct in office and reckless endangerment. Porter's manslaughter trial ended in a hung jury in December.

Maryland Judiciary spokeswoman Angelita Williams said in email that no appeal documents have been filed.

Gray was a 25-year-old black man who was fatally injured in police custody. Six officers were charged in his arrest and death.