A conservative political commentator published three photographs on Monday that appeared to show excerpts from writings by the shooter who killed six people at a Nashville Christian school, enraging parents of the surviving students and prompting an investigation into the leak.

For months there has been a court battle over whether any of the assailant’s writings should be released, with the families of about 100 students who survived the shooting at the Covenant School in March having sought to prevent their publication.

The larger trove of documents — which one city official quantified in court as “voluminous” — has remained with the Metropolitan Nashville Police Department as the legal battle winds its way through the courts. But on Monday, Steven Crowder, the political commentator, published three photos of handwritten notebook pages that appeared to have been left behind by the shooter and reflected a hateful, calculated plan to target the private school and its students.

The Police Department later confirmed that it was involved in the investigation into “the dissemination of three photographs of writings,” adding that the photos in question were not formal “crime scene images.”

The release of the images was hailed by high-profile conservative lawmakers in Tennessee and on Capitol Hill, who have said that keeping the writings from public view was akin to a cover-up. In a video discussing the images, Mr. Crowder said his staff had reviewed the photographs from an undisclosed source and had worked to verify their authenticity, framing their release in part as an effort to force transparency.

But his move stunned city officials, leading Mayor Freddie O’Connell, who was sworn in to his role in late September, to order an investigation into how the images had been released.