The police chief in Dallas, Texas has defended his decision to kill a suspected shooter with a bomb delivered by a remote-controlled robot.

Sniper bullets killed five officers and wounded seven others during an otherwise peaceful protest in the city on Friday. Chief David Brown told reporters that negotiation attempts failed.

“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 police chief also said the shooter had material for explosives and talked of using homemade bombs during the standoff.

That deadly combination set the stage for what many experts say is the first time US law enforcement has used a robot-delivered bomb to kill an active shooter. Robots like these are typically used to defuse explosives rather then deploy them.

“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,” writes journalist Cyrus Farivar for the ArsTechnica blog.

“To me as someone who’s looked at the use of military technology and law enforcement technology, it’s yet another example of what is often called the ‘green to blue’ pipeline,” says Farivar. “For years we’ve been taking about how there are many types of military weapons that are now entering local street level law enforcement ... so now we’re entering a world where not only do cops have bomb disposal robots because they’re worried about bomb situations but they’re employing some tactics that were pioneered by American forces in Iraq and Afghanistan to turn those robots into bomb delivering devices.”

.@DPDChief talks about the robot that was used. pic.twitter.com/ffMf8CD5qa — Dallas Police Depart (@DallasPD) July 11, 2016

Chief Brown says that by the time Dallas police deployed this robotic bomb, they were out of other options. Five officers had already been killed; civilians had been wounded.

Others say using a robot to kill sets a disturbing precedent.

Farivar says the thinking shouldn't end there. “While I think that it’s disturbing and gives us pause, I think the real question we have to think about here is: What does this look like the next time a police department wants to do this? Should there be policies, or rules or standard practices, under which law enforcement agencies would deliver a bomb to kill somebody?”

“As a society, I just think we have to ask ourselves if we want to engage in this type of tactic. We should all be very clear how these things get deployed.”