British police seem to be experiencing a very unusual -and hard to fathom- delay in identifying the type of explosive used in the London bombs.
"Forensic experts are scrutinising the four blast sites to determine the exact make-up of the substance... Early reports suggested the bombers had used a military plastic explosive during the attacks on the capital's transport network.Perhaps the coyness is because the truth would poke a hole in the official line about homemade bombs. A line at variance with early accounts by some media sources.
"It was later claimed that police had found acetone peroxide - or TATP - in a bath during a raid on a property in Leeds.... However, the source said police were still carrying out tests to establish its exact make-up." [Source]
So how hard is this identification process? Not very.
Within hours of the blasts, early examination of the scene by explosives experts would have already narrowed down type of explosive used. The blast velocity is the clearest indicator.
This can be determined from visual inspection of damage to metal panels and gross structures; also from close examination of the penetration power of explosive metal fragments. An experienced eye could quickly make an educated guess.
Simple chemical tests would narrrow the options still further. And mass spectrographic analysis could not only identify the explosive, but can even potentially tell how it was manufactured -by identifying contaminants in the explosives.
It is hard to imagine how it would take more than 24hrs. to be pretty certain, maybe 48hrs. to be definitive.
It's been just two weeks.
See Also: French Terror Cop Leaked Bomb Plot Truth