"The FBI's involvement in the probe now depends totally on Washington," a top police official told The Daily Star asking not to be identified.

Trung Vu, a special agent, flew in Dhaka Wednesday evening, two days after the US ambassador had met the prime minister in response to the government's request for FBI assistance to probe the grenade attack on an Awami League meeting in Habiganj. The attack left AL lawmaker and former finance minister Shah AMS Kibria and four others killed and about 70 injured.

The prime minister on Monday gave assurance that all cooperation would be provided to the US government if it decides to assist in the investigation, said sources.

The FBI special agent met different government high-ups and held meetings with home ministry officials Thursday to work out terms of reference specifying the assistance requested for and its parameters.

A diplomatic source said both sides agreed upon most of the terms and hoped to reach agreement on the rest. Details of the terms of reference however could not be known.

After talking with the CID (Criminal Investigation Department) officials involved in the probe, Trung took with him a Habiganj border map, photographs of the AL meeting venue before and after the attack and copy of statements of people arrested in connection with the attack.

He is likely to submit a report to his office on his Bangladesh tour, specifying which and how many experts are required to come to Bangladesh, in case Washington finally agrees to involve the FBI in the probe, said the source.

Dhaka formally requested for FBI assistance on January 29. The next day US Assistant Secretary of State for South Asia Christina Rocca called Foreign Minister M Morshed Khan and said it was important that the US receives clear terms of reference for the assistance.

Rocca said the terms should include full access to all evidence and witnesses to make the FBI enquiry effective.

On Sunday, a highly placed home ministry source told The Daily Star the government has no objection to providing the FBI with full access to evidence and witnesses and that it is awaiting Washington's response.

State Minister for Home Affairs Lutfozzaman Babar and Home Secretary Omar Farooq could not be contacted over phone for their versions despite repeated attempts last night.

The FBI is responsible for the protection of the US and its citizens from any terrorist attack. Investigation into violations of federal criminal laws and providing guidance and law enforcement assistance to federal, state, local and international agencies are also among its tasks.