The National Police Association and other groups are suing to make the writings and other materials of mass shooter Audrey Hale public in the month since the deadly Covenant School killings.

The NPA filed a lawsuit against Nashville and Davidson County to make Hale's manifesto public. Authorities have held on to the materials during their ongoing criminal investigation into the March 27 massacre that killed three children and three adults

The Tennessee Firearms Association also filed an administrative appeal for the materials, The USA Today Network reported. 

NASHVILLE SCHOOL SHOOTING: 6 KILLED INCLUDING 3 STUDENTS, SHOOTER DEAD

Audrey Elizabeth Hale

Suspected school shooter Audrey Elizabeth Hale, 28, was shot dead by police on March 27, 2023. Hale penned a manifesto before she unleashed a barrage of gunfire at The Covenant School in Nashville, Tennessee. (Metro Nashville Police Department)

The NPA is requesting text messages and communications to and from the Nashville Police Department regarding Hale's writings. 

"It has been more than a month since the shooter was killed and the officers involved have been praised for their actions in the incident," Doug Pierce, a lawyer for the NPA, said. "Accordingly, there is no criminal case and there is no reasonable likelihood of there ever being a criminal case arising from this incident."

"The Metro Nashville Police Department has sought to rely upon a rule of Criminal Procedure to deny public access, but those Rules only relate to a 'criminal proceeding," Pierce added. 

Memorials for the six victims who were killed in a mass shooting are placed outside of The Covenant School

Memorials for the six victims who were killed in a mass shooting are placed outside of The Covenant School in Nashville, Tennessee on Tuesday, March 28, 2023. On Monday, three adults and three children were killed inside the school. (KR/Mega for Fox News Digital)

Hale opened fire inside the school with two semi-automatic, assault-style rifles and a handgun before being shot and killed by responding police officers. 

Calls for authorities to release what Hale left behind have grown in the weeks since the shooting. The police department blames litigation for the delay. 

"Due to pending litigation filed this week, the Metropolitan Nashville Police Department has been advised by counsel to hold in abeyance the release of records related to the shooting at The Covenant School pending orders or direction of the court," the department tweeted Wednesday. 

Audrey Hale wears red hat and carries guns as she walks through school hallways

Covenant School shooter Audrey Hale walks past the Children's Ministry desk. (1:57) (Twitter @MNPDNashville)

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Nashville lawyer Wally Dietz said in a statement Wednesday that the city is asking the court to give victims' families a chance to appear and raise concerns or objections about the release of the writings, The USA Today Network reported.