New evidence shows former Hamas commander Mahmoud al-Mabhouh was given a fast-acting muscle relaxant before he was assassinated in one of Dubai's luxury hotels in January.
Forensic tests have found a substantial amount of succinylcholine in al-Mabhouh's system.
The drug is often used by doctors to administer a breathing tube in patients, but experts believe al-Mabhouh was given it before being suffocated so his death would look more natural.
Israel's Mossad secret service has been widely blamed for the murder, although the country has refused to confirm or deny involvement.
Associate Fellow at the London-based Royal Institute for International Affairs, Rime Allaf, believes the perpetrators underestimated detectives in the UAE. "I think it shows how little aware they are of the capacity of other intelligence services and other police networks. Clearly they had not expected the excellent work of the Dubai Police," she said.
Dubai has linked at least 26 suspects to al-Mabhouh's death. They reportedly entered the United Arab Emirates with fake European and Australian passports. Several of the suspected killers share names with Israeli citizens.
Britain has launched its own inquiry into the use of fake British passports in the operation.
British police officers are currently in Israel, but Allaf doubts anything substantial will result from their investigation. "I think we have to be realistic. The governments have had to react. I f only for the sake of their own populations and their own media to show that they would not be letting another country misuse and abuse their relations. But I would not expect the British government to downgrade its relations with Israel, which is a great pity because this is an affront to the British government and an affront to the British people,"she said.
It is still unclear why al-Mabhouh was in Dubai without protection.
Israel says he was a major player in smuggling weapons to Hamas militants in the Gaza Strip, and it is believed he may have been carrying out a planned arms deal.