Now, Dallas police have released additional details about the technology it used to end the standoff.
On Saturday, authorities reported using a Remotec model F-5 to deliver a one-pound payload of C-4 and detonation cord to the target. In a news conference on Monday, Dallas Police Chief David Brown clarified that officials used a Remotec Andros Mark V-A1. He also said that the machine was purchased in 2008 for roughly $151,000. The whole idea was improvised in about 15 to 20 minutes.
The Mark V-A1 is manufactured by Northrop Grumman. It is driven by a human via remote control, weighs 790 pounds and has a top speed of 3.5 mph. It carries a camera with a 26x optical zoom and 12x digital zoom. When its arm is fully extended, it can lift a 60-pound weight. The "hand" at the end of the arm can apply a grip of about 50 pounds of force. Here's a diagram of the machine, from a Northrop Grumman brochure:
A lot of attention has focused on the novelty of using a robot for offensive purposes and what it might mean for future policing, but it's actually very hard to discuss the ethics of this tactic without talking about the explosive used. The bomb type, how it was deployed, and what, if any, collateral damage may have been caused are all integral to our understanding of the incident.
We know that police used a pound of C-4 explosive. What does that mean? Is that a lot? How much damage can that cause?
Well, C-4 is an extremely versatile bomb. Not only can it be used to blow things up wholesale, it can also be molded by hand to produce directional explosions. That allows users to punch holes through objects or break other things cleanly in two.
Asked by his officers how much C-4 to use, Brown said he trusted their judgment.
"I said, 'Don't bring the building down,'" he said. "But that was the extent of my guidance."
Unfortunately, without knowing whether or how the police had used a shaped charge, it's more difficult to know what the effects of the blast were. C-4 would probably have caused a great deal of damage, Matt Barnett, who runs Bonetti Explosives in Columbus, Tex., told my colleague Philip Bump on Friday.
"If I took a block of C-4 in there, or high explosives, there's a good chance I'm going to not just damage this guy really badly, but I'm also going to probably disrupt the building in a really bad way," Barnett said.
When C-4 explodes, the initial shock wave travels at a rate of 26,400 feet per second. A little over a pound of C-4 is enough to blow up a truck, which suggests that the payload used by Dallas police probably did some appreciable damage, although Brown said that the robot itself was not destroyed in the blast. Only the machine's extension arm was damaged, and then only partially.
"It is still functional," said Brown, "if we had to use it for other operations."
Ann Hatch, a spokeswoman for the Dallas County Community College, which runs the building in which the shooter took refuge, told The Washington Post on Saturday that college officials have not been allowed to assess the damage done to the building, because it was still under police control. But, she said, descriptions of where Johnson was killed by police — in a "garage" — are inaccurate. In fact, Johnson was on the second floor of a college building that occupies much of an entire city block.
How did the authorities maneuver their robot bomb there? It's possible that they used a bank of elevators to get the robot to the correct floor, Hatch said.
As a parting note, it's important to point out that "robot" in this case simply means a remote-controlled car with an attached camera and an arm (as well as the bomb). What defines a "robot" in popular language can span a huge range, covering everything from RC vehicles to semi-"smart" machines that can sense and avoid objects to fully sentient Terminator bots. Although descriptive and sexy, the word "robot" has as much opportunity to mislead or hype as to clarify and illuminate. (Just a reminder not to get too carried away with the term.)