An empty apartment block on a quiet street turned out to be the perfect place for the three suspected Brussels attackers to prepare the home-made nail bombs used in Tuesday's airport and metro attacks that killed at least 31 people.
In a building undergoing renovation, there were no near neighbours to notice them taking in large quantities of strong-smelling household chemicals, as well as a suitcase of nails, to concoct an unstable white explosive powder known as TATP, or triacetone triperoxide, that they later used in their attacks.
Having moved in two months ago, the Belgian brothers Khalid and Brahim El Bakraoui used the apartment in the largely middle class borough of Schaerbeek as a laboratory-cum hideout, from where Brahim and two other men took a taxi on Tuesday morning to the airport to commit their attacks.
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Their choice of low-cost explosives - among ingredients are drain cleaner and nail varnish remover - apparent knowledge of chemistry and ability to set up in an apartment 15 minutes drive from the airport should offer clues about IS bombmaking methods to investigators struggling to understand how the Syria-based group built a violent network of radicalised young Belgians.
