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.