Police suspect that the four US nationals had come to Mumbai with some specific mission and "their visit to Malad to address a congregation did not appear to be as simple as it meets the eye".
The US nationals, Philip Allan, Clover Edward, Richard Jenal and an unidentified person, were questioned by the Special Branch sleuths today, before police decided to deport them for violation of visa rules.
The action came after the local police station in Malad submitted a report to the Special Branch.
"The four US nationals will be deported by the next available flight for violation of visa conditions," Additional Police Commissioner (Special Branch), Bipin Bihari, told PTI without elaborating further.
A Special Branch official said that Philip Allan, one of the four US nationals, has a multiple-entry visa and frequently visited India and neighbouring Nepal, Bangladesh and Sri Lanka.
"He is not a business traveller and therefore his frequent visits to India and adjoining countries raises suspicion in the backdrop of the Malad incident," the official said.
Police said the role of a school teacher from Malad, who had arranged the congregation in which the US nationals had participated, was also being probed.
Apart from these four US nationals, there were four more US nationals who were present at the congregation, police said adding that they, however, left India yesterday.
"We would have questioned them too, but laxity on the part of the local police helped them to leave the country," a Special Branch official said.
The official said that prima facie, it could not be substantiated whether the four US nationals belonged to any religious organisation or had visited Mumbai to propagate their religion.
"Yet, there is something fishy about their visit which needs to be probed further," the official said.
The US nationals were attending a congregation on Saturday night, when a group of people allegedly assaulted them. Two persons were arrested in this connection but were released by a local court later.
Special Branch officials, however, denied that VHP or Shiv Sena members were involved in the assault. "This appears to be a spontaneous reaction from the Malvani residents, who thought the congregation was meant for conversions," police said.