Relatives of blast victims at a railway compensation counter. (Reuters)

Mumbai, July 17: Ammonium nitrate is used as a fertiliser and can easily be available at agricultural supply stores or perhaps, in well-stocked garden shops.

In and around the city, glass tubes filled with a brownish gelatinous substance, a mix of ammonium nitrate, nitro-glycerine and sodium nitrate mixed with fuel oil, and locally known as gelatin sticks, are available without any difficulty.

They cost around Rs 50 a stick and are widely used in stone quarries in adjacent Thane. Fishermen also use them to set off blasts in water bodies to catch fish.

Police believe at least 10 to 15 of them were grouped together with a timer to cause each blast on July 11.

“Ammonium nitrate is hard to find in countries like the US (especially after the Oklahoma City bombing) as it is easy to use it as an explosive. But in India, the compound is easily available,” said a senior official of SFL.

Ammonium nitrate had been known as a volatile substance for decades. A favourite of the Irish Republican Army, the substance had been employed as an explosive everywhere from the UK to West Asia.

During the 1970s, CIA officers were taught to build ammonium nitrate bombs as part of their basic training programme, according to an anecdote related in his memoir See No Evil by Bob Baer, a former CIA officer stationed in West Asia. Intelligence experts say the CIA passed on knowledge and skills of making ammonium nitrate-based explosives to their local support networks in Afghanistan during the Cold War era.

A favourite of al Qaida-sponsored local groups now, the bombs are generally known as ANFO bombs (ammonium nitrate with fuel oil bombs). The compound has been used in Bali, Madrid, World Trade Center 1993 and Istanbul.

According to trial documents, Ramzi Yousef who bombed the WTC way back in 1993, had access to extensive documentation regarding the care and handling of ANFO bombs.

In India, it has been a favourite with groups like Simi and have been widely used. The most recent example, perhaps, is the Varanasi blast earlier this year. The series of blasts that rocked Mumbai through 2002 and 2003, used gelatin sticks as explosives.