Homeland Security deployed hi-tech spy plane which scoops up tens of thousands of phone calls at one time above San Bernardino for days after massacre

Federal investigators looking into the San Bernardino massacre deployed a spy plane overhead after the attacks in an apparent attempt to find additional suspects, Daily Mail Online can reveal.

The Department of Homeland Security is said to have put up the single engine craft over the California city and ordered it to make repeated circles overhead.

The craft would likely have been equipped with 'Dirtbox' technology which can scan tens of thousands of phones in one go to identify suspects.

The report adds to the intrigue about whether or not there were accomplices in the San Bernardino attacks, which took place last Wednesday and were the worst terrorist attack on American soil since 9/11.

Sofrep, which first reported the plane's use, said the use of the spy plane showed that law enforcement was 'actively searching for other members of a terrorist cell.'

Eyes above: The Department of Homeland Security is said to have put up the single engine craft over the California city of San Bernardino after terror massacre and ordered it to make repeated circles overhead

Look out below: Jump door on the plane can be used in-flight. This shows craft high above homes

Inside look: Customized controls in the spy plane allow operators to listen in on tens of thousands of phone conversations in one go around

The massacre in San Bernardino took place when Syed Farook, 28, an environmental health inspector, and his wife Tashfeen Malik, 27, murdered 14 of his co-workers and injured 21 at the Inland Regional Center where they had gathered for a Christmas party.

The couple were shot dead by police, who found more than 5,000 rounds of ammunition at their home and a bomb making factory with 12 IED-style devices.

It has since emerged that Malik posted her loyalty to ISIS leader Abu Bakr al-Baghdadi during the massacre and Farook had been in touch with known jihadists.

The Sofrep report stated that the Pilatus PC-12 plane that was used - was similar to the craft deployed by the military on missions over Africa.

Sofrep produced a map of the flight path for the plane which showed numerous circles over the area around Farook's home in Redlands, a suburb of San Bernardino.

I spy: The deployable EO/IR sensor provides the ability to be an observer of unlawful activity 

Detecting terror: Sofrep, which first reported the plane's use, said the use of the spy plane showed that law enforcement was 'actively searching for other members of a terrorist cell'

Every move: Technology in the planes can monitor an entire city and can track a pedestrian's entire journey and the route taken, allowing investigators to track all of their movements

Spy planes have been deployed by the Department of Homeland Security and the FBI before, such as over the protests in Baltimore in August in the wake of the death of Freddie Gray.

A story by the Wall Street Journal described in detail how the two foot wide 'Dirtbox' allows an astonishing level of surveillance once it is up and running.

The device works by pretending to be a cell phone tower - mobiles automatically connect to the nearest one so latch onto the box - and can sweep up data on tens of thousands of phones in one go.

The operator is able to locate a person's location quickly although they are not able to listen to calls.

Jay Stanley, a senior policy analyst with the American Civil Liberties Union, has written about the spy planes and called them 'not your parents' surveillance aircraft'.

He described how fixed-wing aircraft are making use of another surveillance technique known as 'Wide-Area Surveillance' which involved a super high resolution camera being fitted onto the undercarriage of a plane.

Terrorists: Tashfeen Malik, 27, and her husband Syed Farook, 28, murdered 14 of his co-workers and injured 21 at the Inland Regional Center where they had gathered for a Christmas party on December 2

Close watch: Map of the flight path for the plane shows numerous circles over the area around Syed Farook's home in Redlands, a suburb of San Bernardino

How it works: The 'dirtbox' device works by pretending to be a cell phone tower - mobiles automatically connect to the nearest one so latch onto the box - and can sweep up data on tens of thousands of phones

Spy plane: The operator is able to locate a person's location quickly but cannot listen to calls

It can monitor an entire city and can track a pedestrian's entire journey and the route taken, allowing investigators to track all of their movements.

The question of whether or not there were more suspects in the San Bernardino massacre has never been fully resolved.

Farook's neighbors said they saw a number of men coming and going from his house in the weeks up to the attack but did not say anything for fear of being accused of racial profiling.

San Bernardino police initially said that there was a third suspect but changed their minds and said the shooting had been carried out by just Farook and Malik.

However, they later said that a third person had been arrested, Farook's neighbor, Enrique Marquez, 24, who CNN reported had helped him plan to carry out a plot in 2012.

Marquez also bought the assault rifles that the couple used in the shooting.

The addition of the Pilatus PC-12 aircraft to the Homeland Security fleet was reported by Aviation Week as far back as 2004, though the fleet has grown since.

The company's website talks of its 'adaptability to perform a wide range of missions' and an interior which has been designed by BMW Designworks.

There is a 'a fully enclosed flushing lavatory', a baggage area and, unlike other spy planes, the floor is completely flat.

The website states: 'With the ability to integrate this airplane into both your business and personal life, some people have come to call it the ultimate aerial SUV.'

Nobody from Pilatus and the Department of Homeland Security were available for comment.