A grand jury has declined to bring charges against Dallas police officers who killed the infamous sniper that went on a shooting spree during a downtown rally in 2016.

The Dallas County District Attorney's office said in a release that investigators presented their findings to a grand jury more than a year after the July 7, 2016, attack by Micah Johnson, a 25-year-old Army reservist who investigators said was upset by recent shootings of black men by police.

The use of the robot to detonate a pound of C4 explosives near Johnson, killing him, was a first for a U.S. police department.

David Brown, who was the police chief at the time and has since retired, said shortly after Johnson was killed that he made the decision to use the robot because negotiations had failed and he wanted to end the continued threat to officers.

District Attorney Faith Johnson, who has no relation to the gunman, noted that all police shootings are required to be examined by a grand jury.

"Our thoughts and prayers continue to be with the families of those who lost their lives that night, the officers who were injured, and all of the men and women who courageously put themselves into harm's way, all in an effort to protect our community," Johnson wrote.

She added later to her statement, saying, "As with all officer-involved-cases, this case was presented to the Grand Jury to determine if the use of force by police was reasonable given the unique facts and circumstances of the case presented."

The decision appears to conclude the investigation, and a police spokeswoman issued a statement saying the department is pleased with the outcome and hopes to move forward with healing.

Jay Stanley, a senior policy analyst with the national American Civil Liberties Union, said Dallas' use of the bomb-carrying robot to apply lethal force causes concern because when things "get easy to do and become cheap enough to do, they get overdone."

"The Dallas case represented the very first kind of use of remote lethal force. And so I think it's especially important that there be a lot of transparency around it," he said.