A lengthy motion filed Friday in Baltimore City District Court cites a variety of concerns, including conflicts of interest and questions about the office's independent investigation.
"There is no conflict of interest. I'm going to prosecute. I'm the Baltimore state's attorney. My district includes every city in Baltimore city. A number of crimes that take place in Baltimore city and unfortunately in the district we live. Where is the conflict?" she said.
The court document spells out what the defense sees as five conflicts of interest:
1) Mosby and her husband, City Council member Nick Mosby, stand to gain financially and politically.
The couple live in the area where Gray was arrested and Nick Mosby represents the district where much of the rioting and looting took place. The defense alleges he had a personal interest in stopping the unrest and as the husband of the state's attorney was in a position where he could influence the Gray case.
"It is inconceivable that Mrs. Mosby was not influenced by the challenges presented to her husband as community leader of neighborhoods that were literally 'up in flames,' " the document says.
2) Someone in her office has a personal relationship with a potential witness.
, a deputy state's attorney, will be one of the lead prosecutors on the case. She is in a relationship with a Baltimore television news reporter, Jayne Miller
, according to the Baltimore Sun. The investigative reporter was one of the first people to speak to the second prisoner in the police van carrying Gray. Donta Allen told Miller and other media outlets like CNN that he never told police that Gray was intentionally trying to injure himself, as was written in an application for a search warrant. The motion calls for the parties involved, including Mosby, to recuse themselves.
3) Her office took a role in investigating the case.
The defense says it will want to call investigators from Mosby's office as witnesses. But they will be unduly influenced because Mosby is their boss and wants a conviction, the officers' attorneys claim.
4) There is a pending civil claim against her office.
On Thursday, the city and the state each received a notice that the defense believes it has cause to file a civil lawsuit claiming unlawful arrest and detention of the six officers. The officers were justified in their arrest of Gray for an illegal knife, the document says, so detaining them amounted to false imprisonment. The motion also says Mosby's public comments expose her to civil liability. The letters act as a request for a financial settlement for "more than $75,000" for each officer.
5) An attorney for Gray's family, William "Billy" Murphy, is a close friend, supporter and a lawyer who represented Marilyn Mosby in an ethics complaint.
There is no doubt Murphy and Mosby know each other well. He was on her transition team after she was elected to the state's attorney's office. He last year donated $5,000 to Mosby's campaign, according to Maryland campaign reporting records.
The motion says Mosby's pursuit of criminal charges, especially the ones involving the intent of the officers, "potentially has a direct financial impact" on Murphy, who likely will sue on behalf of the Gray family.
The defense also says that because Murphy personally represented Mosby in an ethics case that she has a conflict of interest.
Murphy told CNN on Friday he hadn't read the filing and couldn't comment on the specifics of it.
Call for special prosecutor
The motion also says Mosby "egregiously violated" the officers' rights to due process when she "publicly and with inciting rhetoric" announced the case against the officers by reading every word of the charging documents. The motion also says Mosby's statements to the young people of Baltimore revealed her political and personal motivation in the case and betrayed the U.S. Constitution and ethical requirements of prosecutors.
The motion calls for the case to be dismissed, and if not, for a special prosecutor to be appointed.
Gray was arrested April 12 for possessing an illegal knife and suffered a fatal spinal injury while being transported in a police van to a booking center, Mosby said.
The officers face various charges that could lead to decades in prison.
Officer Caesar R. Goodson Jr., who drove the police van, faces the most serious charge, one count of second-degree depraved-heart murder. If convicted he would face up to 30 years in prison. Other officers have been charged with crimes like involuntary manslaughter or second-degree assault.
The six officers have a preliminary hearing on May 27.
In announcing the charges, Mosby said the incident began when two police officers on bike patrol "made eye contact" with Gray, who then ran.
When officers caught up to him, he surrendered and was placed on the ground, arms handcuffed behind his back. He said he couldn't breathe and asked for an inhaler, but he did not get it, according to Mosby.
Although police found a knife in Gray's pants, it was a variety allowed by Maryland law, and police had no reason to detain him, the prosecutor said.
The motion says the knife was illegal under Baltimore city code.
"If, in fact, the knife was unlawful ... the foundation of the state's argument (that the arrest was illegal) collapses," the document says.
After Gray was arrested he was put in a police van that started off for a police station.
Goodson stopped the vehicle four times over the course of the approximately 40-minute ride to the police station. At the first stop, officers took Gray out, put shackles on his ankles and placed him -- still handcuffed -- headfirst and on his stomach in the back.
At the last stop, Goodson picked up another man who was put in the back of the van on the other side of the partition that keeps prisoners separated.
Mosby said the officers were "grossly negligent" for failing to get Gray medical help, despite his requests, until arrival at the Western District Police Station.
By then, he was no longer breathing.
Gray was rushed to a hospital, where he underwent surgery.
He died a week later.