An explosive hypothesis

It appears that insurgents in Thailand, Nepal, and India are picking up tricks with regard to improvised explosive devices after the recent successes demonstrated in Iraq.

Meanwhile, investigations are underway for the two Russian flights down with interesting results so far. Courtesy of VOA:

In Russia, investigators looking into the cause of two near simultaneous airliner crashes, are focusing their attention on two female passengers, who purchased tickets for each flight at the last minute. On Friday, investigators at one of the crash sites reported finding traces of an explosive...
The body parts of one woman were scattered widely on the ground. Officials said parts of her legs were found in the toilet section of one plane, leading to speculation that she might have detonated some kind of explosive from there.

Other reports have cited hexogen, previously implicated in explosions blamed on Chechen insurgents in Russia, so I did a bit of digging. Hexogen is known by different names.

RDX stands for Royal Demolition eXplosive. It is also known as cyclonite or hexogen. The chemical name for RDX is 1,3,5-trinitro-1,3,5-triazine. It is a white powder and is very explosive.

It's also a component in plastic explosives, such as Semtex.

Stanislav Brebera spent much of his life developing Semtex, the best plastic explosive in the world. It feels like Play Dough, has no smell, and was designed in 1966 to clear land-mines and improve industrial safety. It is also undetectable by dogs and airport security devices...
... this extraordinarily stable compound of RDX (Cyclonite) and PETN (Penaerythrite Tetranitrate) slips through airport security scans as easily as a pair of nylons. According to the FBI, Semtex has an indefinite shelf life and is far stronger than traditional explosives such as TNT. It is also easily available on the black market.
Semtex became infamous when just 12 ounces of the substance, molded inside a Toshiba cassette recorder, blasted Pan Am flight 103 out of the sky above Lockerbie, Scotland, in December 1988... Some experts now put worldwide stockpiles of Semtex at 40,000 tons.

RDX is less stable than Semtex, but more stable than TNT. Given that Semtex has no discernable odor, it's likely hexogen has the similar property. I presume that a belt of explosives would have been caught during routine airport screening. Given the positioning of one of the remains of one of the likely attackers, I'd posit that the explosive and/or detonator was smuggled aboard via a body cavity, and the explosive device assembled while in the lavoratory. It's either that or else Russian airport security was really slack.