Hamas commander Mahmoud al-Mabhouh was found suffocated in his hotel room in Dubai.
CCTV footage released of the assassination shows the assassins following him in the elevator and checking into a room across the hall.
Four of the assassins broke into his room while he was out and pounced on his return.
Dubai has allegedly told Hamas to steer clear of the investigation but Hamas has opened its own investigation with help for Syria and Iran. Hamas would not confirm that Mr al-Mabhouh had been en-route to Iran.