DALLAS -- The criminal investigation into the tragic police ambush that left five police officers dead in Dallas has been officially closed.

Dallas County District Attorney Faith Johnson released a statement on Wednesday, saying a grand jury declined to indict anyone for the use of weapons the night of July 7, 2016.

“As with all officer involved shootings, the Dallas County District Attorney’s Office presented the July 7, 2016 case involving the ambush of officers with the Dallas Police Department and the Dallas Area Rapid Transit Police Department to a grand jury," she said. "The Grand Jury returned a no bill. All evidence related to this case has been returned to the Dallas Police Department. 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.”

Micah Johnson opened fire on police officers who were monitoring a protest through the streets of downtown Dallas. Four Dallas Police Department officers and a DART officer were killed. Nine others were injured, including two civilians.

During a standoff that lasted into the early morning hours of July 8, officers used a remote-controlled bomb robot to kill Johnson. It was the first time a robot had been used by law enforcement in the nation to kill a suspect.

President of the Dallas Police Association, Mike Mata, said it came down to the number of lives that had to be sacrificed.

"We had already given up five [officers] and to get this individual, he was obviously highly trained," Mata said. "He knew what he was doing. And the powers that be made the decision that they knew if they went in with force, that there was a highly likely [chance] that we would have lost more officers.... and was it worth it? And it wasn’t."

There were 111 shell casings found in a hallway inside El Centro College, where the suspect was holed up, police said, and a total of 200 rounds were fired during the ambush.

More than 240 people were interviewed afterward, most of them police officers. Over 100 hours of body camera footage were reviewed, and guns fired by officers were investigated. Police also reviewed about 500 video files, including cell phone videos, private surveillance, and video from the community college.

Since the shooting, it became standard practice for officers to wear heavy vests over their standard bulletproof vests while at protests and other events with crowds.

Mata told us it will still take time for the department to heal, but putting the criminal side of the investigation to rest will help the officers feel a little better.

"Ultimately, it brings closure to the event for a lot of these officers," he said. "Unfortunately, it was a very traumatic event and it’s just another senseless murder that is attached to the city of Dallas. First we had Kennedy. Now we have this."