Police say they have mounted watch on and around the house of the businessmen after they received a complaint from the family and Detective Branch, Criminal Investigation Department (CID), Special Branch and other agencies concerned are working separately to net the criminals.

Several teams have left Dhaka for undisclosed destinations to arrest Kajal and his associates.

Police suspect that the same killers of Shamsul and his son killed Buddhu and Hannan at the Mitford hospital premises Tuesday night and watch trader Rejaul Karim Selim on March 4 in a desperate bid to conceal their identity.

"We are aware of that (Tuesday's killings) and their killing had links to the brutal murder of the businessman and his son," Awlad Hossain, officer-in-charge (OC) of Sutrapur Police Station told The Daily Star yesterday.

"We have had vital information from Guddu (arrested for suspected links to the killing of Shamsul and Russell)," the OC said, "the killings of Shamsul and his son had similarities with that of watch trader Rejaul Karim Selim in many ways," the OC added.

Police retrieved Selim's head and limbs scattered over Srinagar, Louhajang and Munshiganj sadar thanas. Shamsul and Russell's bodies in more than 250 pieces were found in Gazipur and Dhanmondi. All the three were called out before being killed and all of them hailed from Munshiganj. Besides, the arrestees are believed to have links to both the incidents.

A mob allegedly lynched Buddhu, 35, an accused in at least seven cases, on Sir Salimullah Medical College (Mitford) Hospital premises in Old Dhaka Tuesday night after he allegedly gunned down a BNP activist, Hannan, 25, at the same place minutes before.

"Things will get more clear once the killers of Buddhu and Hannan are arrested," the OC added. The OC said Shamsul and Russell were probably killed and the bodies shredded either in Dhanmondi or in Gazipur.

He said Guddu, now on a five-day remand, confessed to having links with Kajal earlier but not now. Guddu also refused his involvement with the killing of businessman and his son.

"We are also trying to find out why the killers adopted such cruel method to kill them," the OC said, adding that there may be three possible reasons -- the killers wanted to conceal their identity or they were on drugs or they wanted to terrorise people in the locality.

OC of Kotwali Police Station ABM Sultan Ahmed however suggested yesterday to journalists that Awami League men might have killed BNP activist Hannan as he had filed a case with them on March 22 after the opposition activists allegedly ransacked the BNP office in Nalgola.

Srinagar police, meanwhile, are interrogating Abdus Samad, a close associate of Kajal, and Tapash, Palash and Habib to gather more information about the killing of businessman and his son. They are also accused in watch trader Rejaul Karim Selim murder case.