In the heart of Venezuela's capital, Caracas, Nicolás Maduro was delivering of a rousing speech. He stood high on a podium, speaking to a parade of military troops.
The event was broadcast live on national TV. An hour in, the Venezuelan president flinched. His eyes widened. An unexpected object flew by.
It was a drone, carrying explosives along the city's historic Bolívar Avenue. Allegedly, this was an assassination attempt using a remote-controlled unmanned aerial vehicle -- the kind of drone you can buy from any electronics store -- fitted with explosives.
Jai Galliott, a nonresident fellow of the Modern War Institute calls the event in Caracas a "modern form of assassination."
Advancements in consumer drone technology mean commercial drones are more stable in the air. They have better communications systems. They can lift heavier loads. At less than $800 online, they're within the means of average people who want to record themselves on an adventure trail, or capture their kid's football game.
Drones are also capable of incredible destruction and, crucially, anyone can get their hands on one. Is it possible to stop bad actors from using drones in terrorist attacks? Answers are difficult to come by.
Off the shelf, into trouble
In 2015, an off-duty employee, reportedly for a US government intelligence agency, showed how easy it was to infiltrate a highly secure building. He borrowed a friend's 2-by-2-foot DJI Phantom drone, and accidentally flew it onto the White House lawn. Officials didn't catch it. The White House's radar was calibrated for bigger threats like planes and missiles.
In 2016, Kurdish forces shot down a small drone in northern Iraq, an unidentified "off the shelf" drone that exploded and killed two fighters when pulled apart for examination.
This January, a swarm of homemade drones fitted with explosives was thwarted by military countermeasures before it could descend on a Russian air base in Syria.
Drones come in many varieties. Most military drones closely resemble planes. The MQ-9, used by the US Air Force, has a wingspan of 66 feet (20 meters). Store-bought drones can fit in the palm of your hand. All have varying degrees of autonomy. Some military drones can fly autonomously, but can't use their weapons to target and kill without a human in the loop. Yet.
"The history of military technology is one of fighting war more and more remotely," says Toby Walsh, an AI professor at the Australian Academy of Science. "This would be the ultimate step, where there wouldn't be any human in there."
The Drone Hunter
In Caracas, after first noticing the drone in midair, Maduro continued his speech. Two minutes later, an explosion thundered overhead. Reports put it at less than a football field away. Bodyguards rushed to surround the president. Fourteen seconds passed, and then a second explosion reverberated two blocks away. The attack injured seven soldiers.
According to Venezuelan authorities, the explosions were caused by two DJI Matrice 600 drones, fitted with 13 pounds (almost 6 kilograms) of C4 plastic explosives -- the type used by military and law enforcement. Maduro's political opponents have been blamed for the attack.
With drone attacks like the one in Caracas and others splashed across the media, people are becoming increasingly aware of the many ways commercial drones can be used.
"Bad guys are turning their minds over that as well," Galliott says. "That's just the risk that comes with any new technology."
Commercial drones are a challenge for security personnel, who must take into account not only stopping the drones, but tracking their origin point.
The main countermeasure used by law enforcement is signal jamming. There are two methods. The first involves jamming the radio frequency used to control the system, typically frequencies of 2.4GHz or 5.8GHz. The second involves jamming the GPS signal drones use to find their way back to operators.
But there are downsides. Jamming the frequencies potentially blocks out all other devices using the same frequencies. Jamming the GPS costs law enforcement the ability to track a drone back to the perpetrator. Worse still, with loss of signal, most modern drones are programmed to automatically land -- not ideal when they've got a bomb attached to them.
Another option: Shoot the thing down. But if there are explosives on board, that's a potential risk to civilians on the ground.
But what if the threat could also be the solution?
Utah airspace security company Forten Technologies has made a drone to take out other drones. The "Drone Hunter" autonomously tracks enemy drones, shoots out a net at 80 mph and drags the drone to a secure location.
Ultimately, the measures taken against a drone are dependent on the context and on what a law enforcement agency wants to achieve.
"It's a complicated area," Galliott says.
Events like the one in Caracas aren't confined to political events, he notes. The beach, open-air shopping malls, airports, football games, all are potential target areas the FBI and local and state police departments should be aware of.
Meet the Predator
The first reported drone assassination attempt came 17 years ago. It involved the US Air Force's Predator drones, not a commercial drone.
It was 2001, less than a month after 9/11. The War on Terror was unfolding in Afghanistan, the US campaigning to rid the country of al-Qaeda. Mullah Omar, supreme commander of the Taliban, was tracked to a building in the southern city of Kandahar. Despite being an untested quantity, despite the blurry rules of using it, the Air Force tasked the Predator with destroying the building and those inside.
It didn't go well. Instead of the building, the propeller-driven spy plane, armed with Hellfire missiles, targeted a vehicle outside, killing several bodyguards. In the ensuing chaos, the Taliban leader escaped.
"If you take the current technology, which is semiautonomous weapons like Predator drones, and remove the human, then you should be very worried," Walsh says.
An international debate among artificial intelligence experts is raging over whether lethal autonomous weapons (LAWs) should be prohibited. This July, 2,400 scientists and artificial intelligence specialists, including Tesla CEO Elon Musk and Walsh, signed a pledge calling on governments to create pre-emptive laws against LAWs.
But Galliott believes the Caracas attack proves the civilian use of less advanced drones is a far more pressing concern.
"That's the point that escapes people with the emphasis on these military systems," Galliott says. "They are high-level systems a civilian could not repurpose without a whole team of people. Whereas these off-the-shelf things, they're available here and now."
Consumer drones are becoming more advanced by the day. DJI, which makes drones mainly for aerial photography, increases the battery life and range of its drones every time it releases a new model. The company's entry-level Phantom 3 quadcopter flies for 25 minutes at a range of a half-mile (1 kilometer). The next step up, the Phantom 4, runs for 28 minutes up to 3 miles.
A representative from DJI says that the company is aware of its drones being used in the Caracas attack, but that the "overwhelming majority of drone pilots fly safely and responsibly."
"DJI makes drones entirely for peaceful purposes and deplores any misuse of a technology that has brought great benefits throughout the world," says Adam Lisberg, head DJI spokesman for North America.
Some safety measures have been put in place.
In the US, drones already have a legal restriction on how high they can fly -- 400 feet. So the solution could come down to "limiting the range of the systems," Galliott says.
He says governments will inevitably need to look at what can be done to control the impact of drones. In Venezuela, authorities have issued arrest warrants for 27 people in the aftermath of the alleged assassination attempt, including military figures and opposition politicians.
The kicker: Anyone could learn to build a similar device. "People are being trained on how to develop these things in high school, university," Galliott says.
Online forums, like MavicPilots.com, are filled with discussions among "amateur" drone builders. "Many actually give guidance on how to remove protections directly programmed into commercial off-the-shelf products," Galliott says, like height or range limits that are artificially imposed.
He warns that it's not beyond the capacity of determined people to build their own systems.
Anyone could turn a drone into a deadly weapon, he adds.
"And that's much more difficult to stop."