The arrested included three women and all the nine were staying in resorts at the sea-side town of Kovalam near here, a city police press release said.
The incident came to light after police, probing a case of three men, claiming to be ''central police'', robbed the Somalian national of USD 3,800 under the pretext of checking him for narcotic substances recently, it said.
The 61 year-old victim had come here for eye treatment and preferred a complaint with the Thousand Lights police, who formed a special team to probe the case.
The police team located the car used by the trio in Kovalam and further probe revealed the accused three persons, besides six others, were put up there for about a month.
''Aadhaar cards in their possession turned out to be fake,'' the release said, adding, they did not have any valid travel and related documents as well.
The gang seemed to be involved in similar offences in and around the city, the release added.