Why not? If Mollen was seen as aiding the American war effort, as he undoubtedly was, then according to Islamic law he was fair game. From Reuters, with thanks to Kemaste:
DUBAI (Reuters) – The group led by al Qaeda ally Abu Musab al-Zarqawi said on Thursday it carried out a shooting attack that killed a U.S. civilian official near Baghdad’s Green Zone government compound.
A U.S. official said on Wednesday that State Department employee James Mollen was shot dead by gunfire. It said he was an adviser to the Iraqi Education Ministry.
“This morning a hero from the al Qaeda group in Baghdad managed to kill one of the American parasites who works as an adviser to the ministry of education,” said the statement from the Al Qaeda Organization of Holy War in Iraq dated on Thursday.