The killers bided their time for days, then weeks, waiting for a moment when American soldiers would be vulnerable.
It came, finally, in the early hours of Sept. 16, 2012. Six soldiers in a Joint Base Lewis-McChord cavalry squadron had an overnight assignment at an observation point. They watched a valley they suspected enemy fighters were using to lob mortars into the soldiers' small forward base near Afghanistan's southeastern border with Pakistan.
The soldiers' thermal imaging scopes let their eyes cut through the dark for several hundred yards. It was a huge nighttime advantage over the enemy.
The trouble was, their enemies at this moment were behind them, only a few feet away, disguised as their friends.
Six members of the Afghan National Police, also stationed at the watch post, climbed quietly atop a small wall, raised their guns and fired at the Americans, according to soldiers and civilians familiar with the Army investigation into the attack.
Three Lewis-McChord soldiers were killed that night: Sgt. Sapuro Nena, Pfc. Genaro Bedoy and Pfc. Jon Townsend. A fourth soldier, Spc. Joshua Nelson from Fort Gordon, Ga., also died.
The attack in the Mizan district of Zabul province marked the single deadliest "green-on-blue" insider attack against American forces in 2012, according to the Long War Journal's catalog of such incidents. It was by far the worst insider ambush of a Lewis-McChord unit in Afghanistan during a year of heavy deployments from the base south of Tacoma.
The betrayal in Mizan still burns among the soldiers who knew the fallen men. As the months pass, they continue to replay the moments leading up to the attack.
"Not a day goes by I don't think about what I could have done better to help prevent that," Capt Brian Rieser, who commanded the Mizan soldiers, said at a February gathering where officers and senior enlisted soldiers reviewed their just-completed deployment.
The first reports of the killings that night had murky information suggesting it could have gone down in a moment of passion, or perhaps during an outside enemy attack on an American position.
But commanders of the unit recently gave detailed accounts to The News Tribune of how it was carried out: A group of Afghan police either joined the security force with the intent of killing Americans from the inside, or they bowed to pressure from the Taliban to do so.
All told, more than 50 Western service members died in insider killings in 2012. But the ambush near Combat Outpost Mizan was so severe, and it followed so many other similar attacks, that it led the Army to shut down partnered operations with Afghan forces for two weeks. This undermined the transition to Afghan control of the country -- the very reason for the sustained U.S. presence in what has become America's longest war.
"After Mizan, the Army itself became more risk averse," Rieser said. "We shut the doors to the (forward bases), which is probably the worst thing."
In late September, then-Defense Secretary Leon Panetta and Joint Chiefs of Staff Chairman Gen. Martin Dempsey held a press conference to announce the resumption of partnered patrols with Afghans.
They acknowledged the Taliban had been using insider attacks to sow distrust among the allies.
"The Taliban is clearly trying to split us apart, but it won't work," Dempsey said.
The top officer in Zabul at the time of the attack was Lt. Col. Jim Dunivan, who led Lewis-McChord's 1st Squadron, 14th Cavalry Regiment. Today Dunivan sometimes questions his decisions to send his men to the fatal observation post.
But he maintains he and his Mizan leaders made the right call, placing the team in that location to deter other threats that had surfaced in the previous week.
The mounting dangers came in the last three months of their deployment, just as they were preparing to hand over the small combat outpost in Mizan to the Afghan army before returning to Lewis-McChord.
"We were doing everything right according to doctrine, and everything we had done over the previous nine months validated what we were doing," Dunivan, 42, told his officers and senior enlisted soldiers at the February discussion.
He urged them not to blame themselves for the deaths of Nena, Bedoy, Townsend and Nelson.
"You've got to smack down the demons," he said. "That wasn't us. We didn't give a uniform to the Taliban. We didn't kill our brothers.
"That was an enemy," he said. "That was a thinking enemy that found a weakness and exploited it."
Changes in the U.S. partnership with Afghan security forces quickly followed the attack, reflecting concerns about last year's rising number of insider killings.
The Afghans "did not take it lightly," said now-retired Col. Charles Webster, who led all U.S. forces in Zabul and southern Kandahar provinces last year.
"They were ashamed it happened, because they know the amount of effort the coalition puts in to support them," said Webster, who was in charge of Dunivan's squadron and Lewis-McChord's entire 3rd Brigade, 2nd Infantry Division on his last tour.
The Afghans took greater pains to screen their recruits and weed out suspicious service members. Both sides enhanced cultural training to avoid offending each other.
It worked well enough to persuade American leaders to continue sending their soldiers out with their Afghan partners.
Today, insider attacks remain a threat in Afghanistan. Two NATO service members were killed last weekend when an Afghan soldier reportedly turned his gun on them.
But the number of attacks has tapered off, and no single ambush since last September's observation post killings has shed as much American blood.
Looking back, Dunivan and his soldiers contend they were targeted after months of hard fighting in a sliver of Zabul province that looked so stable at the time that American forces were rushing to put it under complete Afghan control.
In the end, they handed it over to the Afghans in spite of the Americans' reservations about Taliban influence there.
Mizan did not always look so violent to the Lewis-McChord cavalrymen who served there last year under Dunivan.
He took command of the small combat outpost in Mizan in late March 2012. He planned to station about 40 soldiers there, assigning them to protect higher-ranking Army advisers and support Afghan-led missions.
Dunivan would mostly work out of Qalat, the capital of Zabul province, about 25 miles from Mizan. He was on the road constantly, covering ground previously controlled by Army units that had triple the 600 or so cavalrymen he now commanded.
The News Tribune followed him on his first visit to Mizan, finding widespread optimism among the ranks of Alaska-based soldiers who were handing the outpost over to Dunivan's troops from Lewis-McChord.
"Mizan is open for business," crowed Command Sgt. Maj. James Coroy, the top enlisted soldier leading the departing troops, in that spring 2012 visit.
Coroy felt confident that the newly secured Mizan-to-Qalat road would stay open under the protection of Afghan National Army soldiers. This, in turn, would speed the withdrawal of American forces from that corner of the country.
Back then, a spirit of openness prevailed between the American and Afghan sides of the compound. U.S. soldiers would drop in on their Afghan allies to get loaves of local bread.
Lt Jason Oberoi of Lacey, a young officer on his first combat tour, used a kitchen metaphor with a News Tribune reporter to express his optimism about the handover of authority to the Afghans.
"The cake is almost done baking here," Oberoi said.
The optimism diminished within a month. Dunivan's soldiers encountered surprising resistance as they probed the villages around Mizan alongside large units from the Afghan National Army.
On May 3, the Afghan army moved into a nearby valley with some 200 local soldiers; four Americans from Dunivan's squadron followed along as advisers. They found about 20 entrenched Taliban and foreign fighters protecting an apparent drug deal.
Taliban fighters fired machine guns and rocket propelled grenades from tree tops and behind mud walls, shredding the Afghan government soldiers, breaking morale and threatening to send the local troops home in full retreat.
The Afghan army front line broke and the Taliban fighters took an Afghan medic captive when he tried to rescue one of his soldiers. The Taliban executed him.
The Afghan soldiers and U.S. advisers never anticipated such a hard struggle in the valley. The Afghan army had selected the target, and it had not encountered so many enemy fighters there previously. U.S. commanders said the area had far more opium -- a cash crop for the Taliban -- than they expected.
"That was a major hot spot," said Sgt. Joseph Stout, 27, one of the advisers from Lewis-McChord.
Stout and his peers from the cavalry squadron joined what turned into a nine-hour shootout. He led charges of Afghan soldiers into Taliban-held tree groves to recover the executed Afghan soldier.
The Americans also called in earth-shaking air strikes and gun runs from Apache attack helicopters. The air power tilted the battle to restore the Afghan army's momentum.
Stout was one of three soldiers from the Lewis-McChord cavalry squadron who received medals for valor stemming from the fight that day. A fourth soldier has been nominated for a medal.
They returned to their forward base knowing they helped prevent a severe embarrassment for the Afghan army in Mizan. They were proud to do their jobs well under fire.
"Listening to those guys talk, it was perfection. Everything was flawless," said Staff Sgt. Shaun Meads, 31, of Lakewood. He relayed their messages to commanders at a Zabul province aviation hub.
Yet they also learned that securing Mizan would not go as smoothly as they'd anticipated that spring. They saw firsthand that the Taliban could surface at any time amid the craggy peaks surrounding the Arghandab River in the Mizan district.
"We definitely found out the Taliban owned that area," Stout said. "They owned the people, they owned the police, and the (Afghan National Army) wanted them out."
A month later, Dunivan had a hunch that another Afghan-led mission in Mizan might benefit from a few extra soldiers from his unit. It was an assignment that would use helicopters to drop American and Afghan soldiers on high ground in hostile territory.
Within minutes of touching down, a Colorado-based major stepped on a mine. He was evacuated and survived.
Five days of summertime fighting followed against more than 30 Taliban. At one point, insurgents fired on the U.S. and Afghan government troops from four directions.
"That was pretty much constant contact," said Dunivan, who was there for the first two days of the battle.
Around the same time, the Taliban laid so many mines in the road connecting Mizan to Qalat that it became virtually impassable.
Despite the threats, Dunivan had many reasons to feel good when he took his mid-tour leave in July.
He had been in Afghanistan for more than half of his yearlong deployment as squadron commander, and he had not lost a soldier to a fatal attack.
"I had almost in the back of my head thought, 'Hey, I'm going to get these guys out of here without losing anybody.'"
They racked up successes, such as the day they found a Taliban bomb-making factory.
Better yet, Dunivan saw his soldiers developing virtuous partnerships with Afghan police and army forces. His cavalrymen built confidence in the Afghan government and deferred to Afghan leaders in setting priorities.
In one incident in Mizan, Lewis-McChord soldiers led by Lt. Oberoi calmed tensions between Afghan soldiers and civilians after an attack on the local troops. The Americans got between Afghan soldiers seeking to round up nearby civilians.
"We gained street cred for ourselves out there. The word got out in the Mizan Valley that the (Afghan security forces) at COP Mizan were the good guys," said Rieser, who had direct responsibility for the soldiers stationed at Mizan.
Dunivan's soldiers repaired roads and irrigation ditches they inadvertently damaged with their heavy vehicles. Civilians welcomed them in most places they visited.
He likes to tell the story of a cavalry medic who bandaged a wounded Taliban fighter before taking him into custody.
"If you were a bad guy, we were going to kick your ass. If not, you were going to be glad we were there," he said.
During his home leave, Dunivan met with Army families and told them: "We are being successful as a squadron because we are treating Afghans with respect."
Back in Zabul for the final months of his tour, Dunivan knew he'd have to close down the outpost in Mizan and hand it over to Afghan forces.
He suspected his troops would be vulnerable in that transition; the Taliban are known to put on a show when U.S. forces hand over their positions, as if to suggest to locals that the insurgents drove out the occupying force.
Dunivan took steps to protect Mizan during the handover by doubling the number of U.S. soldiers stationed there. About 80 were packed into the tiny outpost.
On Sept. 10, mortar fire started pouring in. Ten rounds fell that night. Eight more followed on Sept. 11, according to a summary of Mizan attacks provided by Maj. Donald Braman, the squadron's current executive officer.
Dunivan said he couldn't let those shots go unanswered. There were too many soldiers consolidated in too small a space to risk more mortar rounds.
He split his Mizan soldiers in two groups, sending about 25 to an overlook position called Spin Murani a little more than a mile away. He kept the rest in the main outpost on the Mizan valley floor.
That strength was divided further when the Spin Murani unit broke off six soldiers to hunker down in an overnight observation post about a quarter mile away. Six Afghan police officers joined the Americans in the post.
It didn't look like much -- just a dugout covered with tent-like camouflage meant to protect the soldiers from the weather. A wall about 3 feet high surrounded them. Soldiers stocked their post with guns, ammunition, night-vision goggles and gear to intercept enemy communications.
The Americans clustered at the front, either resting or scanning the valley below for enemy movements.
On Sept. 16, about 1 a.m., their six Afghan allies mounted the wall and unloaded their guns, according to verbal descriptions of the attack from Dunivan and families of fallen soldiers.
It's not clear if the ambushed U.S. soldiers managed to return fire from inside the dugout. The Afghans had the high ground and the element of surprise on their side.
Meanwhile, the 20 or so cavalrymen down at Spin Murani knew something had gone wrong when they heard about 15 to 30 seconds of shots from automatic weapons at the observation point.
The soldiers moved carefully up the hill to find four comrades with mortal wounds and two more with severe injuries. One Afghan police officer lay dead on the ground, too.
Medical evacuation helicopters flew in, whisking the survivors to a combat hospital at Kandahar Air Field. Dunivan and his command group arrived within an hour from Qalat, making their way to Mizan on that once mine-ridden road.
The two survivors could not agree who killed the Afghan police officer.
One survivor, a soldier who trained at Fort Gordon in Georgia and joined the Lewis-McChord unit in Afghanistan, maintained that an American had killed the turncoat.
The other survivor belonged to Dunivan's Lewis-McChord squadron. He reported that five of the Afghans turned on one of their own when the man did not shoot the Americans. The American unit believed that Afghan had a friendly relationship with Nena.
The five killers got away, fleeing into the valley. They used darkness, bad weather and the ensuing shutdown of partnered patrols to cover their tracks.
Dunivan's soldiers had been familiar with the threats of insider attacks. They heard reports all year about Americans dying in this way. They knew to keep their weapons at the ready in the company of their partners.
But he believes his soldiers in the observation point didn't stand much of chance. American service members as a rule do not shoot allies unless they know for sure they're threatened.
"I could have been up there, and I could have been awake, and I could have watched six police stand up and until I saw five of them pull up (their weapons), I'm not going to do anything," he said.
"I'm not going to shoot first," Dunivan said.
Dunivan's squadron joined the rest of the Army in pausing on partnered work with Afghan allies through the rest of September and some of October.
He remembers his men stewing in their grief and anger.
Rieser felt his relationships with Afghan battalion commanders suffer. They knew why the Americans could not work with them.
"The longer we stay inside, the longer we hang our heads," Rieser said at the February leadership discussion.
In late October, they handed over the Mizan outpost and mustered together for one last mission in Zabul province: joining with Afghan allies to patrol a neglected road.
Some of the U.S. soldiers did not want to go out with the Afghans again.
"You guys didn't want to do it," Dunivan said at his February talk with his officers and senior enlisted soldiers. "I grabbed your commander by the throat and said, 'You're going to do it.' We weren't going to leave Afghanistan on that note."
The last mission went well. The September insider attack would not be the cavalry squadron's last memory in Zabul province.
Investigations into the green-on-blue attack were completed on both the American and Afghan sides. The Afghan government fired the police lieutenant who oversaw recruiting and daily operations in Mizan.
Webster said Afghan security forces deeply wanted to catch the culprits.
The Stryker brigade commander said the green-on-blue incident took place in the midst of a much-larger, classified Afghan National Army operation in Zabul province that focused his attention as well as the top ranks of Afghan security forces.
In Mizan, he said, the attack disrupted a spirit of cooperation between U.S. and Afghan forces that lasted throughout the deployment.
"It really upset our partners incredibly," Webster said.
The News Tribune filed a Freedom of Information Act request for the Army's investigation in January and it has not received the report. The Army also declined to release a summary of the investigation.
Dunivan and Webster would not confirm whether it led to any disciplinary actions against soldiers and leaders in the cavalry squadron. Webster, now retired from the Army, called the report "a search for the truth, not a search for blame."
Dunivan has been trying to keep his soldiers from pointing fingers at themselves.
"I did not need an investigation to determine fault or assess blame or retribution -- as a leader I do that to myself beyond anything that can be imposed from the outside," he wrote The News Tribune in an email.
When the cavalry squadron gathered for its annual ball at a SeaTac hotel in February, it left an empty table for its five fallen soldiers from the Afghanistan deployment.
The symbolic meal was dedicated to the men lost in the observation post attack, plus Sgt. Michael Ristau, who was killed in July by an enemy bomb. It included lemon and salt to mark their bitter fates.
That ceremony led into another tradition. Cavalrymen decked out in Stetson hats and gold spurs on their boots poured different kinds of alcohol into a barrel, each representing a different phase of their regimental history.
Red wine for Belgium in World War II.
Whiskey for the Midwest.
Sand for Iraq.
Tequila for a stint on the Mexican border -- and more tequila for tequila's sake.
A night of toasts and celebration followed.
"The task was ours, we did our duty, and I could not be more satisfied and proud of what we have accomplished together," Dunivan said in his remarks to the soldiers and their dates. "And I can never thank you enough for your sacrifice and service to our nation, to the squadron and to each other."
Dunivan has since passed his command to another officer and is moving to a new assignment in Germany this summer.
The night of the ball, he had a little unfinished business from Mizan. Some soldiers who earned medals for valor in combat had not yet received them from their command.
One of those men, Spc. David Matakaiongo, was a survivor of the Mizan insider attack. He suffered wounds to his legs in the shootout, and he leaned on a cane for much of the night at the ball.
Dunivan called him forward to the center of the hotel ballroom to receive his combat infantry badge. The medal signifies that a soldier took fire from the enemy and returned his own.
Matakaiongo dropped his cane and walked straight ahead. He held the straight-backed parade pose as Webster, his Stryker brigade commander, pinned the badge to his dress uniform.
Matakaiongo's comrades stepped up to give him a long, loud cheer. They knew what he had seen.
The cavalry finally was home.