Robotics expert Peter Singer of New America also told the Associated Press he believed the use was unprecedented.

But while there are likely to be intense ethical debates about when and how police deploy robots in this manner, Stoughton said he doesn’t think Dallas’s decision is particularly novel from a legal perspective. Because there was an imminent threat to officers, the decision to use lethal force was likely reasonable, while the weapon used was immaterial.

“The circumstances that justify lethal force justify lethal force in essentially every form,” he said. “If someone is shooting at the police, the police are, generally speaking, going to be authorized to eliminate that threat by shooting them, or by stabbing them with a knife, or by running them over with a vehicle. Once lethal force is justified and appropriate, the method of delivery—I doubt it’s legally relevant.”

Police forces have adopted remote-controlled devices for a wide variety of tasks in recent years, from tiny to large. These tools can search for bombs, take cameras into dangerous areas, deliver tear gas or pepper spray, and even rescue wounded people. Police used one small robot in the manhunt for Boston Marathon bomber Dzohkar Tsarnaev. In May, the Dallas Police Department posted on its blog that it had acquired new robots. Other law-enforcement agencies have experimented with flying “drones,” again more correctly remotely controlled aerial vehicles. So far, those uses appear to have been solely for surveillance. The Department of Justice said in 2013 that it had used drones in the U.S. on 10 occasions.

In a few cases, forces have used remote-controlled devices to deliver non-lethal force, too, as Vice reported last year. In Albuquerque, New Mexico, in 2014, “the Bomb Squad supported APD’s SWAT Team on November 9 at a local residence. The SWAT team requested robot assistance to assist on a barricaded subject armed with a gun. The Bomb Squad robot was able to deploy chemical munitions into the subject’s motel room, which led to the subject’s surrender.” Vice cited other news reports that involved hostage situations where robots were deployed, though the applications are sometimes vague. A remote-controlled device could also be equipped to deliver a flash-bang grenade, used to disorient suspects.

Brown didn’t explain what kind of explosive DPD attached to their device. While a department might stock flash-bangs, explosives for breaching doors, and a few other explosive devices, “I’m not aware of any police department having on hand something that is intended to be used as a weaponized explosive,” Stoughton said.

Use of remote-controlled devices by law enforcement raises a range of possible questions about when and where they are appropriate. The advent of new police technologies, from the firearm to the Taser, has often resulted in accusations of inappropriate use and recalibration in when police use them. Stoughton pointed out that prior to the Supreme Court’s 1985 decision in Tennessee v. Garner, the “fleeing-felon rule” gave officers the right to use lethal force to prevent a suspect in a serious crime from escaping. But the justices limited the rule, saying that firearms meant the rule was no longer current. Unless either they or civilians are in danger of death or serious bodily harm, police can only use non-lethal force to stop a fleeing felon. Similarly, the adoption of the Taser has raised questions about whether officers are too quick to use the devices when they would be better served to deescalate or use their hands.