Mahmoud al-Mabhouh was found dead in a hotel room in Dubai
Foreign Secretary David Miliband has said that the use of six fake UK passports by the alleged killers of a Hamas commander in Dubai is an "outrage".
As diplomatic tensions continue to mount over the killing at a luxury hotel, the BBC's security correspondent Gordon Corera explains some of the major issues around the case.
How did the story begin?
The story begins with the discovery of the body of Mahmoud al-Mabhouh in a Dubai hotel room in January.
For the following weeks speculation about how he died and who might have killed him was largely confined to the Middle East.
But when Dubai police held a press conference this week the story moved to a new level, as the police surprised the world by identifying a team of at least 11 people involved in the assassination.
Police revealed CCTV of the hit team carrying out surveillance of al-Mabhouh and even following him to his hotel room.
Some used disguises. They all carried European passports.
Who was the target and why was he killed?
Mahmoud al-Mabhouh was a Hamas commander who was alleged to have been involved in shipping arms to Hamas. He was also thought to have been involved in the killing of two Israeli soldiers in 1989.
Because of his background, Israel clearly had a motive for wanting him killed, although some have suggested others may have also had a motive.
Why is Israel under suspicion?
As well as having a motive, Israel has a track record of assassinating or trying to assassinate its enemies. For instance, in 1997 it tried to kill the Hamas political leader Khaled Mishal in Jordan. On that occasion Israeli agents were caught using Canadian passports.
On this occasion a number of the British citizens whose identities were stolen also lived in Israel.
How easy would it have been to fake the passports?
The British passports used in this operation appear to be sophisticated. The numbers and names match real passports belonging to British citizens, although the pictures and signatures are different.
Creating such a sophisticated fraudulent passport is not simple.
What have been the international implications?
So far, Britain and Ireland have summoned their Israeli ambassadors to ask further questions about Israel's involvement, but the diplomatic fallout has been limited.
That's partly because investigations are continuing and in the UK that process is being led by the Serious Organised Crime Agency. The conclusions of their investigation will be crucial in determining how serious this row becomes.
What are the likely outcomes?
If Israel is proved to be behind the killing and fake passports then we can expect a tougher diplomatic response and perhaps some kind of tougher action.
But no-one is sure what the conclusions will be.