The intruder, identified as Padma Girirao Shekhar, who hails from Kerala, told investigators that he did this for "publicity". However, police are verifying his claims.
The case has been transfered to the Crime Branch which usually probes underworld cases and serious offences.
Shekhar, hailing from Kochi, tried to force his way into the Mint Road headquarters of the apex bank in South Mumbai at around 4:15 pm, before he was overpowered by security personnel, police said.
Shekhar was then taken to the nearby MRA Marg Police station where police teams from th Maharashtra Anti Terrorism Squad and Crime Branch grilled him.
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According to sources, Shekhar, a graduate, came here from Kerala yesterday and was staying as a paying guest in a hotel in Fort area of south Mumbai.
Retired Maharashtra DGP D Sivanandan, who is a security advisor to RBI, visited the police station and later told the media that the investigators were verifying if the intruder has any criminal background in his home state.