Sources said Wilson, also a forensic expert who arrived on Wednesday, has focussed his investigation on the evidence he collected from the bulletproof sports utility vehicle of Hasina, which was riddled with bullets and grenade shrapnel while carrying her to safety.

A few more FBI officials having expertise in other related fields of investigation may arrive in Dhaka for a thorough inquiry of the grenade attack, diplomatic sources said.

The FBI will submit a primary report to the government based on the test results.

Two Interpol experts -- American Marash Vucilaj, a specialist on public safety and security, and Chinese Xin Hu, an expert on terrorism -- also flew in Dhaka on Wednesday to join their Interpol colleagues Jeffry Eyles, an expert on public safety and terrorism affairs, and Jacqueline Pullums, a US analyst of civilian terrorism.

The sources also said the foreign assistance in the ongoing investigation may be extended further as diplomats of a good number of countries are concerned over the recurrence of bomb attacks that claimed scores of innocent lives and destabilised the law and order.

The sources said the scheduled visit of Counter-Terrorism Coordinator of the US State Department Cofer Black on Sunday is 'very significant'. Black may discuss with the government about providing more US help to stop terrorist activities and deadly bomb attacks in Bangladesh and help it bring the culprits behind the incidents to justice.

Black, who had a long career with the Central Intelligence Agency (CIA), is scheduled to meet Hasina and Foreign Minister M Morshed Khan before leaving on Monday.

He is responsible for US efforts to improve counterterrorism cooperation with foreign governments and plays a leading role in the State Department's taskforces to coordinate responses to international terrorist incidents.

Wilson yesterday had a long meeting with Inspector General of Police (IGP) Shahudul Haque at the police headquarters and they talked about the developments of the ongoing investigation, according to sources.

The IGP refused to say what they discussed in the meeting. On arrival of more FBI officials in Dhaka, he said, "At present I don't see any possibility of more FBI officials coming here. However, they may come if they feel it necessary for investigation."

Wilson has come to examine the bulletproof vehicle and there is no possibility of his visiting the carnage scene, a high police official said.

The FBI official and four Interpol experts held a series of meetings with the investigators of six local intelligence agencies yesterday.

An investigator said they and the Interpol experts are still examining the evidence they have gathered and are now collecting relevant evidence and information.