The anti-terror and central intelligence teams from Karnataka, Delhi, Uttar Pradesh and Gujarat said that the persons responsible for the blasts were inexperts earlier but however succeeded in making bombs as time passed by.
“The group has improved a lot in bomb- making techniques over the period and the triple blast would give them the needed confidence to go ahead with more such attacks in future," said a senior official, Anti-Terrorism Squad.
Two people from Bhatkal and two from northern Karnataka were detained by the ATS-Crime Branch for further probe.
An unexploded bomb was detected at Chinnaswamy stadium, Bangalore in Apr 2010. The bomb did not explode as the trigger assembly was defective and detonator came out.
A bomb exploded at Dashawamedh ghat, Varanasi killing a child and many injured.
The next target was Delhi High Court where the bomb did not explode, but experts believe that the bomb had the potential to kill many.
“It is apparent from the blast at Dadar that a nervous member of the group lobbed the bomb on top of a bus stop instead of planting it in a crowded place like Zaveri Bazar or Opera house," said sources.
The back-to-back Mumbai blasts left 20 dead and at-least 131 injured.