The first boots on the ground in the explosives-rigged apartment of Aurora, Colo., shooting suspect James Holmes were actually robot tracks. Fortunately for police, military and emergency responders, bots are showing their mettle in this and other dangerous situations and helping keep their human handlers out of harm's way.

Holmes, a former Ph.D. neuroscience student at the University of Colorado-Denver, alerted law enforcement to the booby traps in his apartment the morning of July 20, shortly after being arrested for shooting dozens of moviegoers taking in an early screening of The Dark Night Rises. While some teams investigated the crime scene and tended to injuries and casualties—12 people died as a result of the shooting—other local, state and federal police officers, firefighters and bomb-squad experts converged on Holmes's nearby apartment to evacuate neighbors and search for additional evidence.

The first order of business at Holmes's apartment was to send in an Adams County Sheriff Department's bomb-removal robot through a third-story window so the bot could disarm a tripwire guarding the apartment's front door. "That robot was really skillfully driven by one of the Adams County bomb techs," FBI special agent in charge James Yacone said during a news conference the day after the shooting. The robot then neutralized potential improvised explosive devices, incendiary devices and fuel found near the door, Yacone added.

After eliminating the initial threat, the robot's camera was used to search for computers or any other evidence that the bot could remove before attempting to disarm additional explosives. Evidence taken from the apartment was sent to the FBI laboratory's Terrorist Explosive Device Analytical Center in Quantico, Va. The robot's camera also revealed multiple containers with accelerants as well as what appeared to be additional triggering mechanisms, wires and fuses throughout the suspect's 75-square-meter apartment.

Law enforcement would later find inside the apartment 30 aerial shells filled with gunpowder, two containers filled with liquid accelerants and numerous bullets left to explode in the resulting fire, Reuters reported Tuesday. "This apartment was designed to kill whoever entered it," Aurora Police Chief Dan Oates said during a July 21 press conference. Fortunately—thanks to the robot, dozens of emergency responders and Holmes's odd tip-off following the shootings—the threat was mitigated.

Scientists and investigators from the FBI's Quantico-based Critical Incident Response Group (CIRG) worked with the Aurora police and fire departments, the federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), the Denver Police Department and others at the scene. In situations when local law enforcement requires assistance identifying, diagnosing and disrupting real or suspected explosive devices, CIRG typically responds by sending bomb technicians from its Hazardous Devices Operations Center. Each of the agency's field offices—Denver being the closest to Aurora—has at least one special agent bomb technician on staff.

On Monday, an additional bomb-disposal robot was dispatched to a potentially related threat on the University of Colorado-Denver's Anschutz Medical Campus in Aurora, where Holmes may have shipped some of the items used in Friday's attack. Upon inspection two suspicious packages were later deemed harmless.

Bomb-squad robots typically have a low center of gravity and are no larger than a shopping cart. They weigh several hundred kilograms, maneuver on a set of tracks (some can roll on wheels as well) and can be controlled either remotely or by a bomb technician using on-board controls. The robots—which cost upwards of $150,000 each—are usually equipped with a two-prong mechanical claw, cameras and a two-way microphone for communicating with anyone in the immediate area of an explosive device.

U.S. military operating in Afghanistan and Iraq have come to rely heavily on thousands of robotic bomb detection and disposal units in recent years to protect troops from improvised explosive devices. Bots are also increasingly used to prevent humans from being exposed to hazardous materials. Several were sent to the ruined Fukushima Daiichi nuclear reactors in Japan last year to capture video so that inspectors could assess the damage from a safe distance.

Images of FBI bomb disposal robots courtesy of the Federal Bureau of Investigation