The Dallas police ended a standoff with the gunman suspected of killing five officers with a tactic that by all accounts appears to be unprecedented: It blew him up using a robot.
In doing so, it sought to protect police who had negotiated with the man for several hours and had exchanged gunfire with him. But the decision ignited a debate about the increasing militarization of police and the remote-controlled use of force, and raised the specter of a new era of policing.
The Dallas police chief, David O. Brown, said officers had used one of the department’s “bomb robots,” attaching an explosive device to its arm that was detonated early Friday when the robot was near the gunman. “Other options would have exposed the officers to grave danger,” he said.
But the decision to deliver a bomb by robot stunned some current and former law enforcement officials, who said they believed the new tactic blurred the line between policing and warfare.
They said that it might have been an excessive use of force and that it set a precedent, adding that they were concerned that other departments across the country could begin using the same tactic.
“The further we remove the officer from the use of force and the consequences that come with it, the easier it becomes to use that tactic,” said Rick Nelson, a fellow at the Center for Strategic and International Studies and a former counterterrorism official on the National Security Council. “It’s what we have done with drones in warfare.”
“In warfare, your object is to kill,” he added. “Law enforcement has a different mission.”
Other law enforcement officials supported the decision, suggesting they could take a similar approach if the situation called for it. At a news conference on Friday, New York’s police commissioner, William J. Bratton, said that while he was waiting to find out precisely what the Dallas police did, “we have that capability.”
“This is an individual that killed five police officers,” he added. “So God bless ’em.”
The use of the robot and explosive device comes amid questions about whether police departments, which have bought equipment from the Pentagon that was part of efforts in Iraq and Afghanistan, have become too militarized. During the turmoil in Ferguson, Mo., two years ago, local law enforcement quelled protests with military-style equipment, angering many who said they felt intimidated. The Obama administration has declined to stop the Pentagon from selling the equipment, saying that a vast majority of it strengthens local policing.
While Chief Brown offered no additional information about the use of the robot, it appeared that officers had repurposed a remote-controlled bomb disposal vehicle that is normally used to inspect dangerous crime scenes or pick up suspected explosive devices for detonation or dismantling.
The decision to use the robot in this way left many questions unanswered, including whether a sniper could have shot the gunman. Also, it was not clear why the police did not wait him out.
One expert in legal issues and robotics said he thought the use of the robot was justified, and saw little difference between its use and having a sniper shoot from a distance.
“No court would find a legal problem here,” said Ryan Calo, a professor at the University of Washington law school. “When someone is an ongoing lethal danger, there isn’t an obligation on the part of officers to put themselves in harm’s way.”
There are other significant issues that arise when using an explosive device, according to current and former law enforcement officials. Explosions can destroy property and cause fires.
One of the few instances in which a police force used explosives occurred in 1985, when Philadelphia officers bombed the headquarters of a self-styled black liberation group, Move. Eleven members of the group, including five children, were killed, and a fire spread through the neighborhood, destroying more than 60 homes.
The Move explosives were dropped by helicopter. Using a police robot “has probably never been done before,” said Robert Louden, former chief hostage negotiator for the New York Police Department and a former professor at John Jay College of Criminal Justice.
But bomb disposal robots have been used to deliver objects to suspects, hostages and others, or to distract or communicate with suspects.
Last year, a man with a knife who threatened to jump off a bridge in San Jose, Calif., was taken into custody after the police had a robot bring him a cellphone and a pizza as part of efforts to talk him down.
In November 2014, the Albuquerque police used a robot to “deploy chemical munitions,” in the words of a department report, in a motel room where a man had barricaded himself with a gun. He surrendered.
Mr. Louden said he did not think the Dallas police had planned to use the robot to deliver a bomb. Rather, he said, at a point where negotiations with the suspect broke down, the officers in charge had to decide what to do about it.
“Are we going to endanger an officer?” Mr. Louden said about the police officers’ thinking. “Or do we try something that’s a little bit unique, but in all probability withstands legal tests for justification of use of force?”