Kerala Police officials accompanied him on a commercial flight from Mumbai. He was taken straight to a police camp in the heart of the capital city.
Mumbai Police caught him on Tuesday when he was withdrawing money from an ATM. He will be produced before a court here on Friday.
One officer said Marian was not cooperating in the investigation.
Marian and his friends are believed to have stayed at Kovalam in Kerala last month.
Police have also taken into custody a mobile telephone dealer here who reportedly provided Sim cards to these Romanian nationals without securing proper documents.
The Romanian gang placed electronic equipment in the SBI kiosk, which enabled them to get the details of card holders who withdrew money from the ATM. Using the stolen data, they withdrew money from Mumbai ATMs.
Marian said his gang included three other Romanians who have left India.
The Kerala Police has seized Rs 2,00,000 from his possession, a laptop and some electronic equipment.