(CNN) -- Investigators believe two explosive packages found at airports in Dubai and the United Kingdom on Friday were assembled by the same bomb-maker responsible for the device used in last year's failed Christmas Day "underwear bomb" plot.
An explosive substance called PETN was found in each of the devices, a source close the investigation has told CNN.
What does PETN look like?
Pentaerythritol tetranitrate, to give it its full name, is a fine white powder that resembles sugar or salt. It's a highly explosive organic compound belonging to the same chemical family as nitroglycerin.
How easy is it to obtain?
The core chemical in PETN is hard to make or get your hands on.
How dangerous is PETN?
In a controlled explosion carried out last year for CNN by UK explosives expert Sidney Alford, 6 grams (a fifth of an ounce) of PETN punched a large circular dent into a metal plate twice the thickness of an aircraft fuselage.
Alford said he would usually expect 6 grams to punch a hole through the plate. He said it failed to happen on this occasion because half of the PETN burnt off before the explosion itself; also thick ice under the plate would have softened the impact of the blast.
How much PETN was used in the cargo plot devices?
Col. Richard Kemp, the former chairman of the British government's Cobra Intelligence Group, told CNN affiliate ITN that the quantity of PETN used in the latest devices was five times the amount which alleged underwear bomber Umar Farouk AbdulMutallab tried to ignite aboard a Northwest Airlines flight as it approached Detroit, Michigan on December 25, 2009. Sources familiar with that investigation told CNN the working assumption is that AbdulMutallab may have had some 80 grams of PETN.
But Alford told CNN he calculated the latest devices could have contained up to 30 or 40 times the amount allegedly used by AbdulMutallab. "I calculate the volume to be enough to accommodate between two-and-a-half and three-and-a-half kilos of the stuff," Alford said. "That would be a murderous amount in an airplane."
American and British authorities said the explosive devices found in Dubai and the UK were powerful enough to bring down a large aircraft.
How volatile is PETN?
Not very. Although it is an explosive, you have to hammer it or ignite it to make it go off. This makes it perfect for transporting long distances, according to Alford. "It wouldn't go off accidentally," Alford told CNN. "If I was carrying a pocketful of just neat powder in my pocket, it blowing up would be the last of my worries."
How easy is PETN to conceal?
Alford said an advantage of PETN for bomb-makers is the fact that it is easily concealed: "A great potential advantage of powdered PETN is that it could look like a wide range of substances or be disguised as even more -- whereas plastic explosives do look suspiciously like plastic explosives."
Given its appearance and ability to be concealed, PETN is a challenge for airport security officials to detect through usual means such as metal detectors. Investigators say the latest devices were concealed within printer toner cartridges.
How sophisticated are the devices found in Dubai and the UK?
The device found in Dubai was "professionally" loaded and connected using an electric circuit to a mobile phone chip tucked in a printer, police said. The device found at the UK's East Midlands Airport contained a "manipulated" toner cartridge and had white powder on it as well as wires and a circuit board, a law enforcement source said. The devices were designed to be detonated by a cell phone, a source close to the investigation told CNN.
"They are getting technically better," said Alford, who has seen photographs of the latest devices. "As the means of initiation appears to have been mobile telephones, they will go off wherever they happen to be when you dial the number."
But he said the circuitry was "messy," and added: "They are a bit behind the times with explosives."
CNN's Nic Robertson contributed to this report.