The mystery behind the 'drone incident' that paralyzed air traffic at Sussex's Gatwick airport for 36 hours this week - interrupting the holiday travel plans of some 140,000 people and cancelling more than 1,000 flights - is getting more bizarre by the day. After police revealed they had arrested two individuals - a middle-aged man and woman from Crawley - on Friday night - both suspects have reportedly been cleared of their involvement in the crime and released, according to the BBC.

Police are now continuing their search for the mysterious pilot who disrupted plane traffic by flying drones over the Gatwick runway, piloting them within feet of a control tower and even flashing lights at police who had gathered at the scene in what appeared to be a taunting. One detective who has been assigned to the case told reporters that police had recovered a damaged drone near the airport. Investigators will be working with "the forensic opportunities that the drone presents."

"Our inquiry continues at a pace to locate those responsible for the drone incursions, and we continue to actively follow lines of investigation," the detective said.

Gatwick is offering a 50,000 pound ($63,000) reward via the UK's Crimestoppers for any information that might lead to the arrest and conviction of whoever is responsible for piloting the drones. The culprit will ultimately face up to 5 years in prison if found and convicted.

Meanwhile, the army and police have released few details about the techniques they used to resolve the drone issue. But after photographs of three unidentified devices spotted on the airport's roof surfaced in the media...

...some experts are beginning to develop theories about what the devices are and how they were used.

Many have suggested that the Israeli-developed "Drone Dome" was used to jam communications and down the drone, according to the BBC.

It is believed that the Israeli-developed Drone Dome system, which can jam communications between the drone and its operator, was used. However, experts have said it does not enable the person responsible to be tracked down and captured. John Murray, professor of robotics and autonomous systems at the University of Hull, said it could only "take the drone out of the sky".

The Telegraph published a guide to three systems its experts believe may have been used (text courtesy of the Telegraph):

1. Drone detection device

Gatwick deployed Metis Aerospace’s Skyperion, counter drone system, that detects drones and tracks their flight. The device can also track the drone’s operator, in theory allowing authorities to trace the drone pilot. The company is based in Lincoln and arrived on site at Gatwick on Thursday evening. The equipment takes minutes to set up and can track an in-flight drone from about three miles away in seconds. Two Skyperion detectors were deployed at Gatwick giving coverage across the entire airport. Detection equipment attempts to locate a controller by "triangulating" the signals between the controller and the drone to pinpoint where they are geographically. The Skyperion consists of six panels with round, white faces giving 360 degree detection for radio frequencies used by the operators to direct and control the drones. The Skyperion was successfully tested at London Southend airport in May.

2. Drone tracker

Working in tandem with the Metis Aerospace Skyperion is the ‘military grade’ Falcon Shield counter-drone system developed by Leonardo, one of the key players in the aerospace, defence and security industry. The Falcon Shield system can "reliably find, fix, track, identify and defeat the security threat posed by low, slow and small drones," according to its manufacturer. The Falcon Shield consists of two cameras, one for infra-red night-time detection and the other, smaller lens for regular daytime observation. The third lens - the square lens on the right - is a laser range finder. Falcon Shield claims to be able to take control of a rogue drone and land it safely if needs be.

3. Drone jamming device

Obscured by police officers, the third piece of kit seen on the Gatwick airport roof is possibly a jamming device, used to disrupt the signal between the ground operator and the drone. A well-placed source said a jamming device was deployed at Gatwick and which was supplied by the British military. The source suggested the drone jammer was to be used as backup and as a last resort. Authorities had placed Army and police snipers around the perimeter of the airport and had hoped to shoot the drone down or else trace it back to its operator - rather than jam the signal. "We want to capture the drone not destroy it," said the source. Jamming technology disrupts the radio frequencies being used by the controller to direct the drone. Experts describe it as like using a huge blast of targeted noise to block the signals between the controller and the drone.

The jamming device resembles a gun developed by the US military nicknamed the "dronekiller" that can also jam signals and knock drones out of the sky.

Whatever the technology used, we imagine airports across Europe are taking notes: Though the Gatwick drone incident isn't believed to be a terror attack, the massive disruptions caused by a simple drone - something that doesn't require much in terms of capital investment - will inevitably stoke fears of copycat attacks.