Investigation on four grenade attack cases, filed with different police stations during the period, are also reported to have been shelved.

According to police records, six grenades were recovered from Kismat Phultala village in Batiaghat upazila on February 17. Another grenade was recovered from the compound of Khulna thana staff quarters on February 24.

On February 29 last year, a grenade thrown at Khulna city Mayor's Pajero jeep, allegedly by extremists, did not explode. The grenade recovered by police from near the city corporation office was later detonated by army experts.

On March 5 last year, police recovered a grenade from in front of hotel De Luxe at Lower Jessore Road under Khulna thana. It was also detonated by army experts.

Police recovered a grenade on April 17 last year from Arhonghata Bazar under Daulatpur thana. On April 21 in the same year, another grenade was recovered from a brick field at Alka village under Phultala upazila.

A grenade was hurled on the Joint Forces camp at Icegati village in Rupsha upazila on May 23 last year, allegedly by some extremists. But it did not explode.

On November 28 last year, alleged extremist Haridas Pal was arrested from Jalma union under Batiaghata upazila.

On December 10 in 2003, four operatives of New Biplobi Communist Party (NBCP) were arrested with a grenade.

Khulna Police Superintendent Habibur Rahman told this correspondent yesterday that six grenades recovered on February 17 this year from Kismat Phultala village were brought by cadres of outlawed New Biplobi Communist party. But they could not be arrested, he said.

Intelligence agencies are working to find out sources of the grenades, said a senior official of Khulna Metropolitan Police.