On Wednesday, the Sales Tax headquarters received their second fake bomb alert in 10 days, the third incident in three months, said Byculla police. On August 9, at around 11 am, a personal assistant received a call that said ``building mein bomb rakha hain'', triggering off instant evacuation.

The staff -- over 5,000, people -- as well as visitors -- approximately 1,000 -- made a beeline for the gates.

It took the Bomb Detection and Disposal Squad (BDDS) as well as three sniffer dogs five whole hours to comb the building, only to discover it was a hoax.

On Thursday, the woman called S S Kshatriya, Sales Tax Commissioner at his office, and again cried wolf. This time nobody panicked, though a few fire-crackers were set off to spread the scare. Additional commissioner of police, central region, K L Prasad, deputy commissioner of police,zone-III, A Srirao and dozens of other officers searched the area, but came up with nothing.

However, police recovered 19 cracker-bombs from various spots in the building, one of which was a women's toilet on the third floor.

The caller had also apparently called earlier in the year, on May 31, and had caused the building to be evacuated.

``We suspect an insider's involvement in the mischief,'' Prasad said. ``However, we are making efforts to trace her.''

``We have now planned to keep only two gates open and screen all visitors entering our premises,'' said Kshatriya.

The police -- though clueless -- are nevertheless working on two theories: either the caller is a sales tax evader, or is a discontented employee of the sales tax department.

The Vikrikar Bhavan not only houses the sales tax staff but also the office of Maharashtra Public Service Commission (MPSC), Bank of Maharashtra, and rationing department offices.

Meanwhile, a police bomb detection squad was rushed to the Bombay StockExchange (BSE) building today, following a bomb scare. Police said a search of the BSE this morning had so far not yielded any suspicious object.