How they did it: What security agencies suspect:
The security process that was in use at the old parliament building was overhauled after the 2001 attack. The three-tier process that was put in place then was upgraded to four.
A special unit of Delhi Police and a CRPF (Central Reserve Police Force) contingent are posted at the parliament.There other security tiers that involve other agencies including the Central Industrial Security Force and the Fire Service.
The security layers in place involve frisking of visitors and checking in their belongings.. Phones, bags, pens, water bottles and even coins are not allowed and they also have to show their Aadhaar card. Only after this process, the visitors are allotted passes.
The issuing of passes also involve mandatory background checking. The prospective visitors have to show letters recommending their entry signed by a Member of Parliament.
There is suspicion that the two men had hid the yellow smoke canisters inside their shoes, which security personnel physically frisking them must have missed.
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