Allegedly they did all of what you said. However, a Western journalist "embedded" with the US Army division involved in the incident gives a different version of events.

William Branigin of the Washington Post says the vehicle contained 15 people, of whom 10 were killed and two seriously injured.

He also reports that soldiers at the checkpoint failed to fire warning shots in time.

"You just [expletive] killed a family because you didn't fire a warning shot soon enough!" the paper quotes Captain Ronny Johnson as telling his platoon leader. [link|http://news.bbc.co.uk/2/hi/middle_east/2904911.stm|Civilians shot dead by US troops]

This version fits in very well with the comments the troops made yesterday [link|http://www.nytimes.com/2003/03/31/international/worldspecial/31SUIC.html|Anger and Warning After Suicide Attack]
" "Five seconds," he said today, his voice still laced with anger. "They have five seconds to turn around and get out of here. If they're there in five seconds, they're dead."

The soldiers did exactly what they said would do yesterday. It is clear that the American troops were not trained for this and are nervous and trigger happy.