The nature of the explosives: from C4 to powdered masala spice

On 28 April 2009 Wahid Ali, Mohammed Shakil and Sadeer Saleem were found not guilty of conspiracy to cause explosions at their second trial at Kingston Crown Court. They had been accused of carrying out a hostile reconnaissance of London tourist sites on 16/17 December 2004. BBC2's Newsnight carried a report of the acquittal. Richard Watson claimed that the main charge of the 7/7 bombs was a mixture of concentrated hydrogen peroxide and powdered masala spice. At both the first and the second trial Clifford Todd of the Forensic Explosives Laboratory at Fort Halsted in Kent had testified that the bombs were made with ground black pepper. However, according to his testimony on 2 May 2008, no pepper residue was detected at any of the four bomb sites.

For about a week after 7 July 2005, media reports, now hard to find, mentioned the military explosives RDX and its plasticised version, C4. With the discovery of an alleged bomb factory at 18, Alexandra Grove in Burley, Leeds and IEDs at Luton Station carpark, the talk turned to TATP, triacetone triperoxide, or HMTD, hexamethylene triperoxide diamine. Official sources were guarded. The Home Office narrative spoke only of home-made explosives while the ISC went only so far as to specify organic peroxides. For more detail, see The Changing Type of Explosives Used.

At the 21/7 trial chapatti flour and pepper were introduced.

The bombs that failed to explode in London on 21 July 2005 were almost identical to the ones that killed 52 people on the transport network two weeks earlier. But why didn't they go off?

Investigators spent many hours examining the devices used on 21 July and comparing them with the 7 July bombs.

There was only one minor difference - the 7/7 bombers mixed ground pepper into the mixture while the gang two weeks later used chapatti flour.

But Dr Stuart Black, an explosives expert who gave evidence at the trial, said that was not the reason the devices failed to explode.
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Two theories were offered at the trial at Woolwich Crown Court.

The plot's prime mover, Muktar Ibrahim, himself suggested the device would not explode because he had deliberately diluted it with tap water.
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But the prosecution offered another view.
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Hydrogen peroxide is well known among experts as a potential bomb ingredient- but only if used in the correct concentration.

Source: BBC

The 21/7 bomb makers failed to achieve the required concentration whereas the 7/7 chemists apparently did.

Given that pepper was mentioned at three trials, it is surprising that Richard Watson neglected to mention that fact when he claimed that the main charge was masala. Web searches have failed to turn up any reference to masala in connection with 7/7. However, the doyenne of J7 researchers found that during the first '7/7 helpers' trial two '7/7 shopping lists', found at 18 Alexandra Grove, had been presented in evidence and released by the Metropolitan Police Service.


There are three occurrences of masala here: masala/citric, masala + citric and masala (15kg).
Citric acid is used as a catalyst in the preparation of HMTD.


There is one mention here: Dews MASALA (Dews = Dewsbury).

Pepper does not appear in these lists and yet was found in the Burley flat.

'Bomb materials' in 7/7 plot flat
Kingston Crown Court heard explosive materials were found scattered in "disarray" across various rooms at 18 Alexandra Grove, Beeston, which the jury heard was the "principle" site for the construction of the bombs detonated on the London transport network.

The jury, who were shown pictures from inside the flat, heard containers of a mixture of black pepper and hydrogen peroxide, used as the main charge for the bombs, were found sitting in the bath and traces of high explosive HMTD were on the cooker in the kitchen.

They also heard that the floor of the lounge in the flat was covered with bags of clothing and other items including heavy-duty gloves, masking tape, a rucksack and containers full of a "brown sludge", which was the pepper and chemical mix.

Empty bags of ground black pepper were found along with ice-cube bags and ice packs in the kitchen, which the court was told were used to keep the devices cool.

And plastic trays containing bicarbonate of soda and citric acid were also discovered.

Source: BBC

This seems to match up with the explosives found in the Nissan Micra at Luton station car park.

Details of July 7 'bomb factory' disclosed
Four intact nail bombs were discovered in a Nissan Micra left at Luton airport [sic], Kingston Crown Court heard, along with four containers of bomb-mixture and four detonators.

Source: The Telegraph

However, the images released by ABC News, accompanying this story on 27 July 2005 show only white explosives. There were no brown sludge bombs at Luton. There were no white mixtures at Alexandra Grove.

The Counter Terrorism Command of the Metropolitan Police Service has searched several other suspected bomb factories. Traces of explosive were reportedly found at Mohammad Sidique Khan's Dewsbury house and at 111 Chapeltown Road, Leeds.

The sum of £100 million spent on Operation Theseus has failed to establish the nature of the explosives used on 7 July 2005.