In the midst of the brutal ambush of police officers in Dallas on Thursday night in which five officers were murdered and seven more wounded, experts noted an historical "first" – the use of a robot by law enforcement to dispatch a suspect.

Early on Friday morning, Dallas police used a robot armed with an explosive device on its manipulator arm to kill one of the gunmen, 25-year-old Micah Xavier Johnson, a former Army reservist who served a tour in Afghanistan.

A federal official said Johnson "bantered" with police negotiators and did not appear nervous. He indicated he had been preparing for the assault and "wanted to kill white people," particularly white police officers.

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The end of the standoff came after negotiations "broke down" and turned into "an exchange of gunfire with the suspect," Dallas Police Chief David Brown told reporters. At one point, the gunman had told officials "the end is coming, and he's going to hurt and kill more of us."

"We saw no other option but to use our bomb robot and place a device on its extension for it to detonate where the suspect was," Dallas Police Chief David Brown told reporters. "Other options would have exposed our officers to grave danger."

A U.S. law enforcement official said Johnson had no known criminal history or ties to terror groups. The Los Angeles Times reports he had joined several groups that made allusions to the Black Panther Party, including a group called the Huey P. Newton Gun Club, named for the black power group's co-founder. The group, which was founded last year to fight police brutality, teaches its members self-defense and conducts what it calls "armed patrols" through neighborhoods where the police have killed black men.

"We'd never seen him and we don't know him," member Erick Khafre said in a telephone interview. "The gun club isn't affiliated with him in any way."

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Two experts have weighed in their opinion on whether the use of a robot to deliver a bomb is the first of its kind in civilian situations.

"There may be some story that comes along, but I'd think I'd have heard of it," said Peter Singer, a strategist and senior fellow at the New America Foundation who writes about the technology of warfare.

"As far as I know, it appears to be the first intentional use of a lethally armed robot by the police in the United States," confirmed Elizabeth Joh, law professor at the University of California at Davis.

Prior to the Dallas shootings, robot usage for delivering bombs has been limited to the military, which often improvises in the use of its robots to deliver lethal force. Singer says all indications are that the Dallas Police Department did something similar in this case, improvising a surveillance robot to deliver an explosive device. He emphasized he was "in no way, shape or form condemning" the Dallas Police Department's decision at a time when officers' lives were in greater danger than usual.

Singer tweeted mobile robots, commonly called MARbots, were used to detonate explosives during the early days of the Iraq War, but never in domestic policing. He later told the Associated Press a U.S. soldier told him troops in Iraq sometimes used MARCbot surveillance robots against insurgents.

Joh expressed concern the decision to use a robot to dispatch a suspect had been too hasty.

"Lethally armed police robots raise all sorts of new legal, ethical, and technical questions we haven't decided upon in any systematic way," she said. "Under federal constitutional law, excessive-force claims against the police are governed by the Fourth Amendment. But we typically examine deadly force by the police in terms of an immediate threat to the officer or others. It's not clear how we should apply that if the threat is to a robot – and the police may be far away."

That, Joh added, is only one condition for the use of lethal force.

"In other words, I don't think we have a framework for deciding objectively reasonable robotic force. And we need to develop regulations and policies now, because this surely won't be the last instance we see police robots."

The wheeled remote-controlled robot used is presumed to be part of the DPD's bomb-disposal unit. It is equipped with a manipulator arm on top and is not autonomous.

"When there's a suspected explosive device, a suspected IED, you have this device with a robotic arm and a gripper on it," Singer explained. "You might use the device to open up a bag and see if there's a bomb in it. You might use the gripper to disassemble the device in the classic Hollywood movie cut-the-wire way; you might shoot high-pressure water into it, and you might do a controlled detonation."

Singer explained that is why the department had explosives available – sometimes the preferred way to deal with a bomb is to evacuate the area around it and use another bomb to blow it up.

Jason Koebler and Brian Anderson with Motherboard called use of the robot "an unprecedented act in the history of American policing that raises concerns about due process and the use of remotely triggered lethal force by law enforcement."

Koebler and Anderson note, "Improvised device or not, the concerns here mirror a debate that's been going on for a few years now: Should law enforcement have access to armed drones, or, for that matter, weaponized robots?"

Brian Castner, a Motherboard contributor and former U.S. military explosive ordnance disposal technician, said the incident in Dallas "makes him queasy."

Castner, who served two tours in Iraq defusing roadside bombs, said he was involved in a similar case there, when a bomb disposal robot was used to deliver an explosive and kill someone.

"We eventually did it, and I'm still not sure it was the right call."

The New York Post notes, "Departments across the country have been adopting the remote-control robots and using them in the field – for a wide variety of tasks including searching for bombs, delivering tear gas or pepper spray and even rescuing hostages. One popular police robot, dubbed Packbot, was built by Endeavor Robotics and has been used by authorities in numerous operations, including the Boston Marathon bomber manhunt in 2013. After an attack on a Dallas police station on June 13, 2015, officers used an explosive ordnance robot to dismantle one suspect's bags. Still, none of these devices was directly intended or used to injure or kill."

"Technology is a tool," concluded Singer. "Tools are used the way they're designed and then people improvise and find new uses for them."