"Our investigation has revealed the involvement of two former Al-Umma activists close to slain militant Imam Ali, a hardcore militant killed in an encounter in Bangalore in 2002", state intelligence officials said.
The officials said five sympathisers of the Al-Umma, including a real estate businessman, had also been detained by the special teams formed to probe the blast near an auditorium in the city damaging a cycle.
The blast was seen by police as an attempt to create panic ahead of the two-day state-level BJP conference to be attended by senior leaders, including L K Advani and Gujarat Chief Minister Narendra Modi.
Officials said the bomb was sophisticated and had a timer to trigger the blast after three days.
"It has been made by an expert who used a novel technology to link the batteries to the bomb. Instead of spring, which is used in normal timer devices, seating Plate had been used", official sources said.
The real estate businessman was seen moving around the auditorium area under suspicious circumstance by local people.
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Under pressure to act in view of a series of bomb related incidents since last year, including the unearthing of a pipe bomb from under a bridge on the Jan Chetna Yatra route of Advani, police have launched an operation to curb unauthorised possession of explosives.
Meanwhile, in view of the BJP conference, beginning on May 10, Police are conducting checks at vulnerable areas. Bus crew had been advised to alert the police if they spot any suspicious baggage.
Thousands of police personnel drawn from different units are being deployed at various places, including the venue of the conference. Though no specific threat had been perceived by intelligence, a tight vigil was being kept, police added.