Police in Australia have charged two men in connection with an alleged plot to bring down an aeroplane with an explosive device — with one of them believed to have enlisted his unwitting brother to take the bomb onto the plane in his checked luggage.
The men were also charged in connection to a second alleged plot to create a chemical device that would release toxic hydrogen sulphide.
They have each been charged with two counts of acts done in preparation for, or planning, a terrorist act, the Australian Federal Police (AFP) said.
BREAKING: UPDATE - Two Sydney men charged over planned terrorist acts. https://t.co/t8MgHloKXi
The 49-year-old and 32-year-old, from the Sydney suburbs of Lakemba and Punchbowl, were due in Parramatta Court on Friday morning.
In a media conference, AFP deputy commissioner Mike Phelan said the charges related to two plots: an attempt to place a bomb on a flight out of Sydney; and the building of an "improved chemical dispersion device" that would release the highly toxic hydrogen sulphide.
Police will allege the 49-year-old man attempted to place a fully functioning improvised explosive device (IED), which used a "high military grade explosive", on an Etihad flight out of Sydney on July 15.
Police believe the 49-year-old man intended for his brother — who had no knowledge of the plot and has not been charged — to carry the IED onto the plane in his checked luggage.
"We will be alleging the person who was to carry the IED on the plane had no idea they were going to be carrying an IED," Phelan said.
But the device did not make it past airport check-in. Phelan said the weight of the bag in which the bomb was being carried was "one of the components" in it being stopped, but there were several other possibilities as to why the attempt was aborted.
The 49-year-old terror suspect left the airport with the bag, and the components of the IED were later recovered in raids across Sydney, Phelan said.
"We are confident, very confident, that we have found every single component of that IED," he added.
Meanwhile, his brother boarded the flight without the checked luggage and has not returned to Australia.
Phelan added that the bag "did not make it as far" as to go through security screening, but after receiving the information about the plot, the AFP created a mock IED and carried out penetration testing for the post-check in security systems.
"We had 100% success rate in terms of our mock IED being picked up," he said. "So we are extremely confident that given the systems we have in this country, that that IED would have been picked up by security."
Police will allege that a senior ISIS figure sent the components of the IED to Australia for assembly via air cargo. The components originated in Turkey, Phelan said.
Phelan said police would also allege in court that the men charged had attempted to create a chemical dispersion device that would release "the highly toxic hydrogen sulphide".
"This hydrogen sulphide is very difficult to make so I want to make it quite clear that whilst it may have been a hypothetical plot for these people to put forward, we were a long way from having a functional device," he said.
"There was certainly precursor chemicals that had been produced, and some of the components had been produced, but we were a long way from having a functioning chemical dispersion device."
Police added that as part of the investigation, six premises had been searched across Sydney.
Four men were arrested on Saturday July 29 over allegations regarding a potential terrorist attack involving a plane.
A 50-year-old man was released from police custody on Tuesday without charge, and one man is still in custody.
News of the alleged plot caused extra security measures to be introduced at major Australian airports.