NEW DELHI , India ( CNN ) -- Indian police arrested two suspected dealers in black market cell phone chips -- a vendor and a Srinigar police officer -- in the effort to trace how the Mumbai attackers got theirs . An Indian Border Security Force soldier patrols Agartala Airport , Tripura , which is on high alert . Investigators are also taking a closer look at an Indian citizen who was arrested in February with maps and drawings of some of the Mumbai locations attacked last month . The vendor was arrested in Calcutta ; the police officer was arrested in Delhi . Indian officials have said the November 26 attacks that killed 179 people in Mumbai were carried out by outsiders , but these developments suggest that investigators are also looking for homegrown terrorist connections . Indian authorities believe that all the attackers were Pakistanis , specifically blaming Lashkar-e-Tayyiba , an Islamic militant group based in Pakistan but also active in Srinigar , the capital of Indian-controlled Kashmir . The group , known as LeT , has denied any responsibility for the attacks , but the sole surviving gunman told interrogators he was trained by LeT , Indian authorities have said . Pakistani authorities deny that the attackers were from their country , instead blaming what they call `` non-state '' actors . An analyst who studies India-Pakistan tensions believes that this operation was planned and carried out by militants from Bangladesh , Pakistan -- and India . `` They needed people on the ground who could guide them and provided the inside dope , '' said Shuja Nawaz , author of `` Crossed Swords , '' which examines the role of the Pakistani army and that nation 's relations with India and the United States . `` Otherwise , the Lashkar does n't have the capacity to have cased the joints , to have made all these plans and get these people into the target area so effectively . '' The two men arrested on charges of illegally purchasing cell phone SIM cards , using fake identity papers , will be questioned by police who want to know whether they sold cards used by the Mumbai gunmen , according to Calcutta Deputy Police Commissioner Jawad Shamim . SIM cards -- subscriber identity modules -- are portable memory chips that make it easy to switch cell phones . Intelligence experts say they 're used by terrorists to throw their pursuers off the trail . Though Shamim suggested that reporters should not jump to any conclusions about a connection , he acknowledged there were unconfirmed suspicions that one of the slain gunmen carried a mobile phone card activated in Calcutta . `` It 's now up to the Mumbai police to investigate , '' Shamim said . Indian security sources told CNN sister network CNN-IBN on Thursday that a Bangladeshi national bought cell phone SIM cards for the attackers at several locations inside India . An Indian man was arrested along with five foreigners in north India in February with sketches and maps of Mumbai locations that included several of those attacked last month . Faheem Ahmed Ansari , an Indian citizen who carried a fake Pakistani passport , sits in an Indian jail awaiting trial on charges of planning a suicide attack on Mumbai 's stock market and the Churchgate railway station . At the time of their arrest 10 months ago , Amitabh Yash , senior superintendent of police in the state of Uttar Pradesh , called the arrest of the six men `` very significant . '' `` Generally , we catch two or three of them ; the rest manage to escape , '' he said . `` But then , this is also a warning because that tells us how extensive the network is , '' Yash said . `` And you can be sure there will be others . '' Indian security officials have been heavily criticized since last month 's attacks on Mumbai for not heeding the warning signs . CNN 's Harmeet Shah Singh contributed to this report .
Investigators arrest two suspected black market dealers in cell phone chips . Indian man arrested Friday in northern India also under renewed suspicion . Indian security officials have been heavily criticized since the attacks . Mumbai 's top law official 10 months ago admitted government `` lapses '' during India attacks .