Because there have been so many different accounts I looked up a standard reference for those who have died in the Iraq War, Military City
which is connected the Army Times
group of newspapers. This is their article on Casey Sheehan
which reports he died in a fire fight on April 4, 2004 and was awarded a Bronze Star for the action.
What struck me was that he was an artilleryman, not in the infantry. They had already run out of infantry and were cross-training other specialties to fill slots. He died doing a job he hadn't really been trained to do. He wasn't eligible for the Combat Infantryman Badge, but that was the job he was given.
This is the result of Rumsfeld's belief that people are "fungible", that all you have to do is put whoever is available into whatever job that needs to be done, and things will be fine. Rumsfeld doesn't believe that military jobs require specialized training because they are all just "cannon fodder" and "trigger pullers".