Police have recovered 20 more empty cartridges taking to 32 the total number detected in the terror attack at the Indian Institute of Science campus in Bangalore.

The recovery was made by the Forensic Science Laboratory team during their search at the J N Tata auditorium complex in the campus, Bangalore Police Commissioner Ajay Kumar Singh told reporters.

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"The first comparison of the cartridges have suggested that all the rounds of ammunition have been fired from one weapon," he said, disputing speculations that more than one weapon had been used in the attack.

Singh denied reports that his office had received a fax or letter threatening that bombs would explode at the Chief Minister N Dharam Singh's residence and also in a five star hotel.

It was a fact that the threatening letter received by media offices was secured by him and on the basis of it, bomb detection team and sniffer dogs were pressed into service at the chief minister's residence and Hotel Grand Ashoka, where nothing was found, he said.

In the wake of the terror attack, the city police have been contemplating setting up a separate intelligence wing for the city as had been done in some metros and the issue would be taken up with higher ups, Singh said.