In a letter to Baltimore state's attorney Marilyn Mosby, the president of Baltimore's police union claimed she had too many personal ties to the case to remain impartial while investigating the death of Gray, a 25-year-old black man who suffered a mysterious spinal cord industry in the back of a police van.
"I have deep concerns about many conflicts of interest presented by your office in the case," Gene Ryan, President of the Baltimore Fraternal Order of Police said.
"These conflicts include your personal and professional relationship with the Gray family attorney, William Murphy, and the lead prosecutor's connections with the local media," Ryan said.
"Most importantly, it is clear that your husband's political figure will be directly impacted, for better or for worse, by the outcome of this investigation," Ryan said.
Mosby is married to Baltimore city councilman Nick Mosby, who has attracted attention in recent days for his criticism of the media's coverage of looting in Baltimore.
Mosby's office says that her relationship with attorney William Murphy, who donated to her campaign in 2014, does not represent a conflict of interest.
"Hundreds of people donated to her campaign. There is no conflict of interest surrounding Bill Murphy. He is representing the family in a civil case which has nothing to do with the criminal case," Mosby spokeswoman Rochelle Ritche told the Baltimore Sun.
The police union appears to have been unaware that charges would be brought on Friday. The letter, dated May 1, sought for the appointment of a special attorney before charges were brought.