However, another officer who did not want to be named, told IANS: "Their existence has increased greatly after the parliament attack."
Headley had visited several parts of India and done a recce of the Mumbai targets and passed on the inputs to his LeT handlers in Pakistan ahead of the strike. The Nov 26, 2008, attack killed 166 people and injured over 300.
The September 2008 Delhi serial blasts were the handiwork of a sleeper cell that lay quietly gathering information before carrying out the bombings that killed 30 people and left 100 injured. The suspected terrorists who were killed in the Batla House gunbattle were part of a sleeper cell active in the capital to perform the bombings, an officer told IANS.
"The recent attacks in several parts of the country are a pointer to the setting up of sleeper cells by terrorist groups," the officer added.
Delhi Police investigations have helped crack many modules of terrorist groups. A Maharashtra module of Indian Mujahideen, which was involved in the Pune serial blasts this year, was recently uncovered by Delhi Police. The bombing left one injured.
Delhi has seen nine terrorist attacks since the one on the Indian parliament, with the total fatalities being 54 while 367 people were injured.
Delhi Police declined to reveal any arrest figures of sleeper cells.
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