Dallas police officers say they killed Micah Johnson with a robot explosive, the first time one has been used to kill a suspect in the US. But how do they work?

Dallas Police Chief David Brown said the robot was only used after they unsuccessfully negotiated with the suspect 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 the extension for it to detonate where the suspect was. Other options would have exposed our officers to grave danger."

Mr Brown made a point to say that early reports that the suspect committed suicide were not accurate.


"The suspect is deceased as a result of detonating the bomb," said Mr Brown.

Police in the US are increasingly using robots to help defuse bombs and negotiate with suspects but Peter Singer says it is the first time they have used a robot to kill a suspect.

"Yes, this is 1st use of robot in this way in policing," Singer, a technological expert on national security and military issues, wrote on Twitter, when asked by University of California Davis law professor Elizabeth Joh whether Americans had just witnessed "the first use of a lethal robot in American policing."

Singer added that the use of mobile robots - commonly known as MARCbots - to detonate explosives had been observed during the early days of the Iraq War, but never in domestic policing.

Singer later told the Associated Press that when he was researching his 2009 book, "Wired for War," a US soldier told him troops in Iraq sometimes used MARCbot surveillance robots against insurgents.

The robots are mobile, weigh around 25 kilograms depending on the model and have extendible arms that reach a few metres.

There are a number of different models of robots that police use which have sophisticated audio and visual systems.

Police officers use the cameras on the robot to first assess the situation.

A two-way audio system and night vision allows police to be able to communicate with suspects.

The most common use for a police robot is in bomb removal and disposal. While robots are expensive, the cost is small compared to that of human life. Some robots are so tough that they can survive multiple blasts.

If the robot is able to reach the suspicious device, the operator can use the claw to grip the device, lift it and move it to a cleared location for detonation.

Then in cases like Dallas, robots are used in negotiation situations because unless they're visibly armed, they're relatively nonthreatening. Another benefit is that the robot's cameras can continue gathering information while police use the audio system to communicate with the suspect.

In other situations police can use robots to deliver items like food to victims and suspects in hostage situations. Some robots also have sensors that can detect anything from narcotics to biological, radioactive or chemical weapons.

Some robots that are strong enough to drag victims out of lethal situations.

Companies like Remotec and RoboticFX are constantly working to develop new robots for police forces, the military and other organisations that deal with hazardous situations.

Newer models have better maneuverability, longer-lasting batteries, arms with more points of articulation and new accessories designed to help officers perform dangerous tasks.