The FBI officer met senior officers of Thane Police and exchanged information gathered by both the sides about the scam which was unearthed earlier this month.
The staffers posed as US Internal Revenue Service department officials, making a daily turnover of Rs 1.5 crore.
The intensity of the blast was so high that window panes in adjoining buildings were shattered and shocked people were seen running helter-skelter, an eyewitness said.
They would call US citizens and demand their financial and bank details, failing which they would allegedly threaten them with dire consequences, including legal action and jail term
The Central Bureau of Investigation has arrested an Reserve Bank of India official and a JDS leader K C Veerendra, who is also a casino owner, in connection with separate cases relating to alleged illegal conversion of currency post-demonetisation.