A uniformed Iraqi with all the proper credentials walks up to an armored Humvee in Hawijah, levels his AK-47 at the window and fires off a clip, seriously injuring a U.S. servicemember.

The evening before, in Sulaymaniyah, U.S. forces learn of an imminent attack on their forward operating base. Nearly a dozen Iraqi soldiers, including several on gate duty that night, are subsequently arrested as co-conspirators.

“They were going to kill us in our sleep,” one soldier later said.

Around that same time in May, Iraqi soldiers are ambushed on a bridge spanning a railroad yard in Beiji. At least three soldiers in the unit, call them sleepers or spies, are believed to have played a role in the scheme.

“The leaks are there,” said Capt. Hussin Ali Sulyman, commander of the Iraqi army unit in Beiji.

Figuring out which Iraqi security forces are trustworthy and which are not is one of the greatest challenges American troops face in Iraq. The specific number of attacks on friendly forces involving infiltrators is unknown, but it easily exceeds what American forces experienced in places such as Somalia, Bosnia or Afghanistan.

A senior coalition official associated with training Iraqi security forces said Iraqis do their own vetting of prospective candidates, whether it be a police officer, border guard or soldier. When you’re dealing with thousands of individuals, some bad guys are going to slip through the cracks.

“It’s going to happen,” the official said. “You just have to try to protect against it as much as possible.”

That quandary leads many U.S. troops to err on the side of caution when dealing with Iraqi forces. But in doing so, they send their allies mixed signals. It’s as if they are saying, they’re with the Iraqis and want them to succeed, but no one is above suspicion.

“It’s a thinking enemy,” said Lt. Col. Fred Wellman, spokesman for the Multi-National Security Transition Command-Iraq. “Fortunately, we are a thinking army. But you can’t read a guy’s mind.”

Even someone like Hussin draws doubt.

Sgt. 1st Class Rick McGovern, a senior U.S. training officer in Beiji, described the former Iraqi special forces officer as a capable and loyal ally, saying Hussin has proven himself time and again. And yet during a recent large-scale operation, the Iraqi company commander said U.S. planners didn’t let him in on any of the details until 16 hours before it kicked off.

As he spoke of the snub, Hussin was clearly bothered by it. Hussin said insurgents have threatened him and his family, and that he does his best to work with an uncooperative police chief. McGovern, seated nearby, nodded in agreement.

“We know the Iraqi police in this area are corrupt,” McGovern said.

Nine days earlier, at considerable risk, Hussin put on a disguise, climbed into a nondescript car and drove to a police checkpoint on the edge of Beiji.

Hussin, recounting the sting through an interpreter, told police he was trying to find a group to attack Americans. The police officers manning the checkpoint volunteered their assistance.

“Let’s go,” one of them said, offering to guide him to a safe house.

Hussin begged off, telling them he wasn’t quite ready, and then drove off.

Iraqi police “have two faces,” Hussin said. “They work with the bad guys, and they work with the government.”

Work in Iraq is tough to come by, which explains why so many people want to become or remain police officers, despite the danger of an insurgent attack. Even in Saddam Hussein’s time, it was the army, not the police that typically held the people’s trust.

U.S. troops say the local police in Beiji often extort money from motorists at checkpoints or accept bribes from insurgents to look the other way.

“Iraq is a beautiful country,” said McGovern, a Pennsylvania National Guardsman with 1st Battalion, 111th Infantry Regiment. “There are a lot of good people. The problem is they lived with corruption for three decades. It’s hard for them to break away from that.”

Some Iraqi security forces collude with insurgents purely for money, the Americans say. Others do it out of ideology. Sometimes it’s just hard to tell.

Capt. J.P. Dykes, who commanded a 3rd Infantry Division company in Beiji, said one night his men went to a house “to get a [high-value] target and there were two cops there visiting” the target.

In the Sulaymaniyah incident, U.S. soldiers got word of the impeding attack, even down to the hour, according to Capt. Darcy Burt, the base commander.

In the end, the Kurdish intelligence unit that got tipped off detained a few of the conspirators, including Iraqi soldiers. That killed the operation, which involved nearly a dozen soldiers. Burt said it included the Iraqi guards standing between the American base and the attackers.

The infiltrators, Burt said, “were going to let them come through their checkpoint while they were on duty.”

The next day, about 100 miles west of Sulaymaniyah near the town of Hawijah, a uniformed member of the 3rd Oil Security Battalion walked up to Iraqi soldiers and offered to assist on a security detail. They accepted.

The Iraqi troops were providing additional security for a U.S. military team clearing some ordnance, said Maj. T.J. Hull, operations officer for the 1st Battalion, 163rd Infantry Regiment.

Before one Air Force master sergeant could get out of his armored Humvee, the oil security officer approached the vehicle, raised his weapon and fired into the window.

“He basically emptied an AK-47 mag,” Hull said. “He continued to shoot at the window as he was running away.”

One of Hull’s men shot the gun out of the assailant’s hand, and then dropped him with a second shot. Amazingly, both the airman and his Iraqi attacker survived.

Of course, not all units or police departments are crawling with crooks.

South of Kirkuk is a small town U.S. soldiers refer to as “Pleasantville.”

There are about 10,000 people in Laylan, a predominantly Kurdish town with five schools and a sixth for their Arab neighbors. There is an easy pace about the place, which is what led troops to give the town its nickname.

“Education is important to them,” said Staff Sgt. Anthony Fenicottero, an Oregon National Guardsman with 3rd Battalion, 116th Cavalry (Armor). “I’ve seen them go without power and even water to take care of their schools.”