A number of firms in the United States are believed to have been used to transfer money to assassins who carried out the murder of a top official in Dubai.The discovery could be a key breakthrough in determining exactly who was behind the killing of Mahmoud Al Mabhouh, a founder of the military wing of the Islamist movement Hamas.Al Mabhouh was found dead in his room at the Al Bustan Rotana hotel on January 20.Dubai police have released extensive CCTV footage they say shows a hit squad linked to Israeli spy agency Mossad.However, the Israelis have denied any involvement in Al Mabhouh’s death.Twelve British, six Irish, four French, one German and three Australian passports were used by 26 people believed to be linked to the murder, according to Dubai Police.Many of the documents were either faked or obtained illegally.Now, American investigators have identified a handful of US-based companies believed to have been used to transfer money to the suspects, according to a report in the Wall Street Journal.The firms include businesses that match freelance job-seekers with employers and process payments between the two.Authorities have identified financial transfers from several of these businesses into pre-paid, cash-card accounts used by suspects in the assassination, the report said.But, it added that US authorities do not believe the intermediary companies had any knowledge that the money would be used in the plot. It is thought the money was used for operational expenses, such as buying plane tickets.However, the information will now be used to determine who the employers were in the transactions.