A Japanese man has confirmed that his older brother was the dead man pictured on an Iraqi militant group's website.
Militants said their captive was badly injured in the ambush
The group behind the website, Ansar al-Sunna, had claimed to be holding security guard Akihiko Saito hostage.
Mr Saito, 44, went missing west of Baghdad earlier this month after an ambush on the convoy he was protecting.
The militant group had said earlier that Mr Saito was seriously injured in the ambush, in which four other foreign workers were killed.
Japanese news agency Kyodo quoted Hironobu Saito as saying: "I've looked at the images, confirmed that it is my elder brother and told Japanese police and the foreign ministry."
Iraq's Minister of National Security, Abdul Karim al-Inizi, condemned the killing.
Mr Saito worked for Hart Security, a British security firm based in Cyprus.
He was formerly a paratrooper and veteran of the French Foreign Legion.
he was the sixth Japanese national to be killed while working in Iraq.
Japan has 600 troops working on reconstruction projects inside Iraq.
Many Japanese have criticised the mission, arguing that it unnecessarily endangers lives and violates the country's pacifist constitution.