A flurry of shots rang out, a dozen bullets smashed through the windshield, and then the driver's body slipped below the dashboard.

Five marines hopped over the barriers, raced to the vehicle and opened the door. There were no weapons or explosives inside, but the man had taken a bullet to the head.

"He's dead," said Sergeant Christopher Genetti, and turned off the truck's motor. "If this keeps up, the people are going to turn against us."

Genetti and his fellow marines have one of the hardest tasks now facing US troops in Baghdad -- manning checkpoints where any approaching vehicle could be a suicide bomber.

A decision has to be made in a split second, and that decision is not going to be allowing a racing vehicle to get too close.

Five civilians had already been killed at this checkpoint in the previous 24 hours before the latest shooting Friday morning.

"If it's the enemy I'd shoot him in the head," said a weary Genetti. "With civilians, this shit is a problem."

A mirror, metal crate and tables have been laid out to form a barrier to avoid tragedies just like this one -- but there was also the grisly evidence that the barriers are not enough.

Beyond the first barricade was a blue van, its side windows blasted out and chunks of a human brain splattered in the front window.

After the van was a street lamp knocked out and a yellow Nissan minibus parked in a pool of blood.

The two vehicles had driven toward the palace within a half an hour of each other on Thursday night.

The shooting of the blue van left a husband and wife dead. Inside the palace, the woman's body was piled on top in a posthumous embrace.

Three people were killed in the minibus. It was Genetti's team that had shot at the husband and wife. He expressed pain and regret over the incident.

The situation was almost the same as Friday morning's. The van would not stop. They fired off a warning shot and the vehicle picked up speed, they fired again.

Demoralized at how the couple were like him -- they were married, they had children who were probably his age, he thought -- Genetti had to remain vigilant and tough.

Dirty-faced and red-eyed, he watched the road for suicide bombers and guerillas disguised in civilian clothing.

"You feel bad but you can't get soft out here because that will be the time when they kill you," he said.

SPACE.WIRE