Kerry Cahill paced the floor of a classroom at Nazareth College of Rochester, in New York, explaining to the group of fidgety teenagers in blue Rochester Global Citizenship Conference T-shirts why she and her companion, Nader Hasan, were there. They’d come, she said, to offer their perspective on the terrible tragedies that can happen when people become too isolated and misguided. Nader, a compact 42-year-old with thinning hair and sad gray eyes, leaned against the teacher’s desk as if weighted down. He asked the kids if they knew what had happened at Fort Hood. He got a chorus of bland yeses.

“That was my cousin who did that,” he said. His voice grew so quiet that the students had to strain to hear him finish. “My cousin killed Kerry’s father.”

Seventy heads swiveled toward Kerry, a willowy six-foot blonde dressed in gray and black. She nodded with her eyes squeezed shut, as if to say, “Yes, really.”

It had been two and a half years since her father died, and she still sometimes could not believe it. She had spent months preparing for this moment in mid-March, trading emails and texts with Nader and talking on the phone for hours. The two had been invited to speak at a high school conference on religious tolerance, 1,600 miles from the spot where their lives became horrifically intertwined on November 5, 2009. They had come hoping to reclaim some good from the terror of that day.

Kerry showed photos of her dad, Michael Cahill, a big guy with a white beard who looked like Santa Claus. A 29-year-old actress who lives in New Orleans, she grew up the youngest of three military brats. Her father, she explained, had worked at Fort Hood as a civilian physician’s assistant for seven years. He was known to everyone as Doc Cahill and had a reputation for getting soldiers whatever they needed—a correct diagnosis, meds, a pass on redeploying—even if he had to fight for it.

The day Michael died, he had been back at work for a week after recovering from a heart attack. The deadliest shooting ever on an American military base began when U.S. Army major and psychiatrist Nidal Malik Hasan—whose sparse hair and high forehead vaguely resemble Nader’s—tucked a semiautomatic pistol into his combat uniform, along with sixteen extra magazines and a backup revolver, and drove from his grungy Killeen apartment to Fort Hood. He made his way to the Soldier Readiness Processing Center, where medical personnel were assessing hundreds of deploying soldiers. Once inside, Nidal screamed, “Allahu Akbar!” and began shooting into the crowd. Within ten minutes, 32 people were wounded and 13 more lay dead. Nidal kept firing until an exchange of bullets with two police officers left him paralyzed below the chest.

Kerry was in Chicago at the time and watched the news unspool at the home of a friend who happened to have lost his partner during 9/11. She tried calling her father but got no response. She began dialing every Texas hospital reported to be treating Fort Hood victims but found out nothing. The longer her family went without hearing from him, the more she hoped her dad was unreachable because he was in an ambulance or on an operating table. She kept thinking about how she and her mother, Joleen, had asked him if he really felt ready to go back to work.

At 11:15 that evening, an Army sergeant and a chaplain arrived at Joleen’s door, in Cameron. Michael Cahill, they reported, was the only civilian killed at Fort Hood that day. Witnesses would later recall him trying, amid the bap-bap-bap of gunfire, to protect soldiers by grabbing a chair and rushing Nidal. It took six gunshots to fell him. When Kerry received the news from her sister, she beat her fist on her friend’s kitchen table and wailed.

One time zone away, Nader, a successful lawyer in Washington, D.C., was leaving a golf course when he got a call saying that his first cousin had been wounded in a shooting at Fort Hood. The son of Palestinian immigrants, Nader had grown up with Nidal in the suburbs of the nation’s capital. As he pecked out a quick email on his phone to thirty classmates in a local civic leadership program, explaining why he would miss their gathering that night, Nader wondered what kind of kook would open fire at a military base. He sped to his mother’s home, a block away from his own. As he parked, his phone buzzed with a friend’s worried message: Had he watched the news?

Inside, Nader’s mother, Nawal, was weeping. A talking head on TV was reporting that the gunman, who had trained as a terrorist in Syria, was none other than his cousin. Nader’s thoughts pinballed: Nidal? His sweet-faced childhood playmate? The one who wouldn’t take a swing when Nader and his brother brawled? The one who never dated because his parents didn’t approve, who butchered what Arabic he tried to speak, who hadn’t ever been near Syria?

Just that morning, Nader had celebrated the launch of a wounded-warrior support website he’d helped set up for his dearest friend, a Marine who was recovering from being shot in the head by a sniper in Iraq. Now the incongruity was too much. “I have a major hero, my best friend,” Nader told me later, “and a major horror, my cousin.”

Nearly a year after the attack, in October 2010, Nawal would travel alone to Texas to hear for herself what her nephew had done. During the second week of Nidal’s Article 32 hearing to determine whether the evidence against him merited a full trial, Nawal entered the cramped military courtroom, dressed in a dark suit and carrying a shopping bag filled with home-cooked Middle Eastern food for her nephew. She looked stricken when he was rolled into the room in a wheelchair.

Sitting across the aisle from her was Joleen. As she struggled to understand what had motivated the man who killed her husband of 37 years, the widow also found herself wondering who the dignified Palestinian woman was. Nawal stared at Nidal’s blank face with as much horror and disbelief as any relative of the wounded or the dead. As soldier after soldier took the witness stand to describe the bloodbath, she appeared to fight back tears.

Nawal kept her silence until the last day. “We want everyone to know,” she told me in the hallway, her whisper edged with exhaustion, “we had no idea.”

Nader and Nidal Hasan, the oldest sons of two Palestinian brothers, grew up practically as siblings. Nader’s parents immigrated to Washington, D.C., in the early sixties and then helped Nidal’s parents follow. The families lived just blocks away from each other, and the two boys were a year apart in age. Nader still remembers playing hide-and-seek with Nidal among women’s clothing racks every weekend as their mothers shopped at the mall.

The family ties began to loosen, however, when Nader’s parents divorced when he was in the fourth grade. Nader, his brother, and his three sisters were raised by Nawal, who worked her way up from a mailroom job to the post of vice president at a Wachovia bank. She loved her adopted country and told her kids that there was no conflict between being a good Muslim and a good American. Nader played football, joined the wrestling team, and got an earring and a mohawk. Though he helped Nidal get his first job, at Pizza Hut, the cousins grew further apart when Nidal’s family moved to Roanoke to run several convenience stores and a diner. Nidal lived at home while pursuing a biochemistry degree at Virginia Tech, clerking at the family stores when not in class. He joined the Army to pay tuition and then went to military medical school, while Nader ended up studying law at the University of Illinois.

Neither young man was particularly devout; though their parents fasted during Ramadan, they were too busy working to be mosque regulars. When Nidal’s father died, in 1998, his son could not recite the Islamic prayers at the funeral. But in 2001, as Nidal’s mother lay dying of Hodgkin’s lymphoma, she begged him to get to know God, and he began attending mosque. After her death, the family saw his interest in religion as a natural part of grieving. Nawal herself had become more devout after losing her sister, even making a pilgrimage to Mecca, and she encouraged her nephew when he spoke of reading the Koran.

A few months after Nidal’s mother’s funeral, terrorists attacked the World Trade Center. Reeling along with everyone else, Nidal adamantly told his family that the hijackers were burning in hell. Nader, for his part, found himself representing Muslim clients who were being questioned by terrorism investigators after the attacks. Because of his connections—he had tended bar at a swanky Republican hangout in the nineties—he was asked by a member of George W. Bush’s press team to guide members of the media at Yankee Stadium when the president made an appearance at the World Series, as a way of showing American Muslim support. He also volunteered at several presidential events in Washington and attended a Christmas party at the White House that year.

It wasn’t until 2006 that Nidal began telling relatives that he wanted out of the Army because he didn’t want to fight Muslims. He also spoke of being disrespected because of his faith. “My retort was, ‘What do you expect?’ ” Nader recalled. “The family agreed it came with the territory.” Their biggest worry was that Nidal had no real friends or pastimes. By mid-2009, he kept so much to himself that nobody on Nader’s side of the family knew that he’d been promoted to major. That October, when Nidal got the orders he’d dreaded—for deployment to Afghanistan—he didn’t tell anyone back home.

Weeks later, on that awful afternoon in November 2009, Nader stared as the TV blared a false report that his cousin was dead. Soon one of his sisters handed him the phone: Fox News anchor Shepard Smith was on the line. In the live interview that followed, Nader told Smith that his cousin feared going to a war zone, was harassed by his military colleagues, and once hired a lawyer to explore the possibility of a discharge. “We’re blown away,” he said. “The guy was born and raised here, my cousin, a good American. Our family is feeling sadness. . . . Our condolences go out. We’re shocked.” When Smith asked if his cousin was violent, Nader sounded incredulous. “Him? No. Absolutely not.”

The next morning, TV trucks besieged Nader’s street. His office was deluged with calls and emails from people who were livid that he’d called his cousin a good American. A retired Secret Service agent, a friend of a friend who had worked at the White House, came to Nawal’s home to keep the media at bay. That same day, Nader and his relatives spent hours with the FBI, telling investigators everything they knew about Nidal. Even then, they could make no sense of what he’d done. Their only certainty was their shame and the sense that they all now bore a permanent stain. Nader’s office lost clients, and one grim morning, an official at the high school where he’d been volunteering as a wrestling coach asked him to pack his things and leave.

In Texas, Kerry and her family also grappled with the aftermath. A week after the shooting, Kerry found herself enraged when she went to a drugstore to buy Ensure for her mother, who wasn’t eating, and saw her dad’s killer on the cover of Time. For a while she avoided magazine aisles. Then she began calling news editors every time she saw the major’s photograph in articles about Fort Hood’s fallen, complaining that the focus on him was disrespectful to his victims. (She claimed a victory when the Killeen paper stopped using his image as the icon for its online coverage.) It also hurt, she told me, when Nidal’s photo appeared in stories about her father being awarded a posthumous medal for bravery. “That’s forgetting the soldiers and the people who died and the people who were there,” she said. “Who we choose to remember says a lot about us.”

Returning to New Orleans helped. Kerry taught in an after-school program and landed small roles on the television shows Treme and Memphis Beat, as well as in the movie Texas Killing Fields. In a city still recovering from Hurricane Katrina, she found it comforting that people knew that coping with trauma sometimes meant crying at traffic lights. In February 2011 she traveled to Washington with other victims’ families for a congressional hearing on whether missteps by the Department of Defense and the FBI had precipitated the Fort Hood attack. But the government’s findings only made her angrier. Nidal’s superiors, the families learned, had worried for years about his mental and emotional stability and his declarations that the U.S. was at war with Islam. Further, the FBI had known that he’d corresponded with a suspected terrorist. (News outlets reported the suspect to be the late radical imam Anwar al-Awlaki.)

Though Nader avoided the hearing, he became just as distressed when he read the congressional report. He’d had no idea how troubled Nidal was. And he was mortified by how few Muslim leaders were stepping forward to denounce the violence or to call extremists what they were: enemies of their religion and their countries. The silence, he felt, compounded his shame. Yes, his life and law practice had returned to normal, but that normalcy now disturbed him. In March, when another congressional hearing was convened to investigate homegrown Islamic terrorism, Nader felt compelled to take action. “I kept saying, ‘Where’s the voice?’ ” he told me. “I decided to own this.” A few months later, despite his family’s misgivings about attracting attention, Nader and several friends created a foundation to encourage American Muslims to voice their patriotism and speak out against extremism. They called it the Nawal Foundation, after Nader’s mother, whose name means “gift” in Arabic. Its slogan would be “No more silence. No more violence.”

The initial response from mosques in D.C. was tepid. Yet Nader felt encouraged when, toward summer’s end, a Pew Research Center survey found that nearly half of U.S. Muslims believed their leaders should speak out more against extremism. A Gallup poll also reported that American Muslims were more strongly opposed to sectarian violence than any other U.S. religious group. A week before the tenth anniversary of 9/11, Nader went on ABC’s This Week for an interview with Bob Woodruff and publicly announced the foundation.

To his astonishment, the response was immediate. Kerry, at home in New Orleans, was so moved when she watched the interview that she sent Nader an email to say that she wanted her family to meet privately with his. “I am hoping,” she told him, “that a meeting would be a beginning.” Other emails and phone calls followed: from Joleen; from Leila Hunt Willingham, whose 22-year-old brother, Jason Dean Hunt, had died in the attack; and from Jessica Zeigler, whose husband, Patrick, had been shot four times and whose recovery had required the removal of nearly 20 percent of his brain.

On the eve of the second anniversary of the shootings, Nader had dinner with the Zeiglers at a restaurant in the D.C. area, and the next day, he met with Leila and the Cahills. As he drove Leila, Joleen, Kerry, and Kerry’s siblings to his house, he pointed out landmarks whose juxtaposition seemed surreal: here was the mosque where Nidal—and, years before, three of the 9/11 terrorists—had prayed; there was the Chinese restaurant favored by the Bushes. When they arrived at his home, Nader’s wife brought out homemade baklava, and the Cahills gave the couple’s toddler son a copy of Michael’s favorite children’s story, Mouse Soup. They’d spotted the book at the train station that morning and considered it a sign. “That was so totally Dad,” Kerry told me.

Nawal was initially too mortified to join them. When she finally did, after some coaxing, she wept and apologized and spoke about her nephew with a mix of bewilderment, anger, and shame. The Cahills hugged her and told her it wasn’t her fault. “I can’t imagine how it must be to have to think, ‘What could I have done?’ ” Kerry explained later. “She didn’t deserve this either.”

The trial for 41-year-old Nidal Hasan will take place in August at Fort Hood. He is being held at the Bell County jail and could face the death penalty if convicted. Though the major receives visits from a relative who lives in the West Bank, Nader has avoided contact with him; he told me he couldn’t bring himself to interact as long as his cousin “took the position that what he did was justified.” Still, the family feels obligated not to abandon Nidal. Nader has recently begun listening in when Nawal speaks to him on the phone, and he plans to visit his cousin sometime in the future.

For many of the survivors and grieving families, however, seeing the major tried is not enough. More than eighty of them have filed a $750 million legal action against the Army and other government agencies for ignoring Nidal’s vocal, violent beliefs. Jessica Zeigler told me that she has been berated by people from Fort Hood for saying publicly that the Hasan family isn’t to blame; one soldier said he’d shoot the major’s relatives if given the chance. “It’s still so fresh,” she said.

All this, says Nader, makes his mission more pressing. In February, Kerry joined his foundation, and together they began planning presentations for Muslim and interfaith organizations. The morning of their appearance at the Rochester conference, news had just broken about Robert Bales, the U.S. Army staff sergeant who has been charged with killing seventeen villagers in Afghanistan. Driving onto the Nazareth College campus, Nader and Kerry spoke about violence and mental illness and the danger of speculating about either, in that case or theirs. “Maybe,” Nader finally said, “it won’t come up today.”

When they walked into the campus gym, they found about four hundred kids from 21 school districts, munching on bagels and ignoring an earnest couple that was playing folk songs onstage. Nader and Kerry burst into giggles; they’d joked for months about singing “Kumbaya” together. Later that morning, however, they were sober—even anguished—as they gave several classroom presentations. “Did they think I knew about it? Did they think I supported it?” Nader wondered aloud to the students, describing his fear that he and his relatives were permanently branded as a terrorist’s family. “Now I have this scarlet letter.” Kerry spoke about how she’d talked to a counselor and one of her mother’s favorite priests and realized she had to make a choice not to stay angry. It sounded simplistic, yes, but her alternatives were worse. “I’m not going to let conflict win,” she said.

“We’re hoping that you can find comfort and strength by seeing what Kerry and I are doing,” Nader said. “That she and I could work together and be friends might seem impossible. And yet we’re doing it.”

The students left wide-eyed. One lingered for advice about being called gay for refusing to fight other kids in his tough neighborhood. Others submitted comments about being labeled terrorists because they were Muslim. Driving back to the airport, Kerry and Nader chatted about the future. The day’s organizers had mentioned bringing them back for another conference. They’ve also been asked to speak in New Orleans at Kerry’s alma mater, Loyola University, and they want to make presentations in Texas. Their discussion included no mention of Nidal Hasan.

“I don’t want to think about him,” Kerry told me. “I want him to be forgotten. What’s important is how we will prevent something like this from happening again. My father stood up, and he died fighting. It’s our turn.”