THE ANSWER: MASKING TAPE AND GOOD OLD-FASHIONED DETECTIVE WORK
With events in Paris still fresh in the memory, both the French police and security services will be trying to track down exactly where the improvised explosives devices involved in the attacks were made.
Having worked on the police investigation into the 7/7 London bombings in July 2005, I wrote a novel based on my experiences, The Theseus Paradox.
Here's what you need to look for:
1. An odd use of a premises
Most people have a routine – they sleep, eat, go to work, have people visit in daytime hours. Bomb factories are often residential homes that are used like industrial premises. People come to work there during the day and then leave in the evening. The bomb manufacturers don’t sleep there. That would be far too dangerous because of the toxic fumes or in case the whole place explodes. And if nobody is sleeping there, that is the big giveaway. Extensive and expensive locks fitted to normal entry doors and odd entry and exit routes will also be important indicators that something unusual is going on. Why is a residential premises being used like a unit on an industrial estate?
The chemicals used to create the home-made explosive devices will have been ‘smelted down’ to make them more concentrated, just as they were in 7/7 and 21/7. The bomb maker(s) will have needed premises with good ventilation, where windows can be opened and where face masks may well have been used.
During the preparation for 7/7, the extremists had to keep the windows of their bomb factory open to let out the toxic fumes. To shield their bomb-making activities from prying eyes, they taped the curtains to window frames using masking tape so the wind didn’t blow them outwards. However, when these places are cleared and cleaned, evidence still remains.
The purchase of brand new curtains is a big giveaway. In the 7/7 investigation, detective legwork led us to one particular property and I was concerned what it had been used for. It was empty, yet had brand new drapes and no net curtains.The replacement curtains led me to spot a tiny fragment of old masking tape attached to the window frame. I knew instantly that something unusual had taken place there. They’d clearly been taping the old curtains to the window frame whilst the windows had been open. We hoovered the carpet and found enough explosive residue contained within one square metre to blow up the entire street.
3. Tell-tale damage
A key signifier of a bomb factory that we saw in 7/7 is bubbled paintwork from the intensive heat involved to make these chemicals more concentrated. When toxic chemicals are ‘cooked’ there are also tell-tale signs such as dying plants inside properties and yellowing foliage outside of windows.
Neighbours and passers-by may have been aware of odd smells and discoloured curtains or hedges. With the 7/7 bombers, it was noticed by their closest associates that some of the hair at the front of their heads had been bleached – we can see the significance of this now, but at the time witnesses didn’t pay much attention to it.
Heating the amounts of toxic chemicals required is very labour intensive and requires a great deal of power. There will have been excessive electricity use for the size of premises which may flag up something unusual going on to the power suppliers. In the 7/7 investigation, we found burnt plug and socket fittings and incidences where the electricity had ‘tripped’ again and again.
5. Crucial exhibits
In 7/7 we found receipts for numerous ‘smelting vessels’, where the bottom of many, many shop-bought milk pans had burned through.
Exhibits such as keys, in particular will be crucial.
In 7/7, we took all the locks out of any doors to premises we knew that the suspects were connected to. We then matched the keys they had to the locks. That way, we could find out if they had keys for premises we hadn’t yet found. That was a crucial part of the investigation.
Police have totally destroyed the scene at St. Denis, finding anything of use there is unlikely after 5,000 rounds of ammunition and a series of grenades. But keys survive bomb blasts and bullets. The main man will still have the keys with him to the premises where they made the bombs, I think.