Early Friday morning, after being attacked by gunmen who had already killed five police officers and injured several other officers along with two civilians in the wake of a protest, the Dallas Police Department deployed a bomb disposal robot.

However, the robot was not used to disarm a bomb. This time, it was used to deliver the bomb that killed one of the shooters—likely an unprecedented move in American policing.

For now, it remains unknown exactly what type of robot or what kind of explosive was used. Authorities have named the dead shooter as Micah Xavier Johnson, a 25-year-old Army veteran from a nearby suburb.

Experts believe this is the first time a robot-delivered bomb was used to take out an active shooter by law enforcement in the United States. The death of Johnson raises new questions about the appropriate limits of drone technology outside of the theater of an overseas war.

The Pentagon has transferred bomb disposal robots to more than 200 law enforcement agencies under the 1033 Program, which transfers military surplus equipment to domestic police agencies, according to the Center for the Study of the Drone at Bard College. The DPD itself acquired new bomb robots in May 2016, according to its website.

“It’s without precedent in the US, but it was not unthought of,” Sid Heal, a retired commander at the Los Angeles Sheriff’s Department, told Ars.

A Marine veteran with four overseas tours under his belt, Heal is now the president of the California Association of Tactical Officers. He added that the LASD had discussed and even practiced similar scenarios as early as 15 to 20 years ago.

In Los Angeles, Heal noted, the decision to deploy a robot as a weapon was rehearsed but never presented to the sheriff himself and never adopted. His agency never actually deployed a robotic bomb in a real-world situation. Plus, these robots aren’t cheap—Heal said they start at about $80,000 each.

“We practiced breaching, we practiced lethal force, we practiced non-lethal, surveillance and reconnaissance,” Heal added. “Here [in Dallas] it was a worse case scenario, and somebody had the foresight and courage to recognize that conventional methods were not going to be successful.”

Indeed, Dallas Police Chief David Brown told reporters at a Friday press conference:

We cornered one suspect and we tried to negotiate for several hours. Negotiations broke down, we had an exchange of gunfire with the suspect, 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. Other options would have exposed our officers to great danger. The suspect is deceased as a result of detonating the bomb.

The DPD did not immediately respond to Ars' request for comment.

Green-to-blue pipeline

It’s not clear if the DPD has a policy that outlined the use of its explosive ordnance robot as a weapon. The DPD used its robot in June 2015 when a man attacked a police station and was believed to have a bomb. Ars has filed a public records request to obtain such a policy and other associated materials.

City records dating to October 2015, located by Asher Wolf, an Australian journalist, show that the DPD has three Northrop Grumman Remotec bomb disposal robots, including a Mark VI, an Andros V-A1, and an HD-2. It is not clear which robot was used to kill Johnson—but all three models are remote-controlled and do not operate autonomously.

Peter Singer, a strategist at the New America Foundation, said on Twitter that the Marcbot, as it's sometimes called, has been “ad hoc used this way by troops in Iraq.” In April 2015, Vice Motherboard made a film showing the American military's experience of outfitting bomb robots as weapons.

It seems plausible, then, that someone in a command position within DPD may have been inspired by military tactics.

A looming specter

The use of machines to kill bad guys still makes many uneasy. For years, America has wrestled with how its largely secret overseas drone program has been used to kill terror suspects, often in remote places.

But Ryan Calo, a robotics law professor at the University of Washington, told Ars that the common philosophical thorns in warfare aren’t applicable here, even though Dallas may be a harbinger of future scenarios.

“This situation differs pretty dramatically from the situation that we’re having from using robots to kill—none of them are present,” he said.

“One thing we worry about is inscrutable kill lists, not so here. [The police] know that this person needs to be killed or in other ways neutralized. The second thing is that do we want to live in a world where robots make decisions to kill? That’s not applicable here. Is a completely robotic army too little of a disincentive to go to war? No, because the officer would have killed him anyway. But it’s hard not to draw the analogy anyway. It’s hard not to think of the militarization of the police.”

But, as he concluded: “I don’t think any policy would have recommended against this use—I’m loathe to second guess these officers.”

Indeed, the decision here seems clear, Heal noted.

“In this case, I’d give away $80,000 if it would keep my guys out of harm's way,” he said.