Ali Bhai, alleged Inter-Services Intelligence (ISI) agent arrested from an eatery in Bowbazar on Thursday, had “probably managed to penetrate some quarters of the armed forces”, police said on Friday.

After interrogating Ali and accomplice Muzaffarul Islam, a hawala operator held along with him, police concluded he had been keeping an eye on the movement of forces boarding the Jammu-Tawi Express from Sealdah. Ali used to run a travel agency at Sealdah.

A floppy and some documents recovered from Ali have revealed that he had already despatched some strategic information to Karachi, sleuths said. “Such information cannot be gathered without the help of an insider,” said an officer working on the case.

Officers from other agencies, including the army and the enforcement directorate, reached Lalbazar on Friday to interrogate Ali. Border Security Force (BSF) officials are expected “in a day or two”.

Sleuths logged into Ali’s e-mail account on Friday and traced five mails that he had sent to Karachi in the past four months. “Ali would use two particular cyber cafes in central Calcutta,” said an officer of the detective department, adding: “Ali told us that he had been paid Rs 40,000 by the ISI in the past three months for passing on the information.”

Sleuths also found a host of telephone numbers, ranging from Lucknow to Burdwan, Malda to Murshidabad.

“We are trying to track down all those whom Ali contacted,” said Peeyush Pandey, deputy commissioner of police (detective department).

This includes a relative in whose Sonarpur house he had been holed up for the past six months.

The trio arrested with riflescope at the airport on Thursday has, however, been given the clean chit. “They visit the city frequently and supply these items to licensed gun-shops,” said an officer.