Jacob Campbell and his grandmother were in a dark movie theater in Sayville, N. Y., waiting for a screening of his film, “Those Left Behind,” about his quest to know his mother, who died in the Sept. 11 attacks. But before the film was screened, Jake and his grandmother, Jeanne Maurer, 85, would have to white-knuckle it through “9/11: An American Requiem,” a 2011 documentary with harrowing images of towers spewing black smoke and fire and witnesses talking about jumpers.

As pictures of destruction flashed on the screen, Jake, 25, whispered to me. “Tell her she doesn’t need to do this,” he said. Jeanne was sitting on the other side of me with her eyes squeezed shut. Her fingers plugged her ears.

Over the past quarter-century, Jeanne had done her best to steer clear of such footage. What she could not look at, though, Jake cannot avoid. That is in part because he grew up on the internet, where such images were inescapable.

But it is also because, through the passage of time and a relentless series of challenges, he had come to realize that he had no choice but to look squarely at all that had shaped and haunted him since the very beginning of his life.‘Something Was Off’The morning Jill died, at age 31, her parents, Jeanne and Joseph Maurer, had come to her Middle Village, Queens, apartment as usual. As their daughter put on her makeup and dashed for the train, Grandma Jeanne and Grandpa Joe waited for 10-month-old Jake to wake, then fed him and drove the few blocks back to their house. When they arrived, there was a message on the answering machine. “An airplane hit the World Trade Center, the other tower,” Jill’s voice said. “We’re all safe,” she said. “I don’t think they’re even evacuating us.”Jeanne turned on the television.

Then she and her husband watched a plane hit the South Tower, exploding through the 78th floor, where their daughter worked as an administrative assistant. In the following days and weeks, Jeanne vacillated between hysteria and magical thinking, convinced that Jill was roaming Manhattan with amnesia. Joe, a retired Fire Department captain, knew better. “My husband, from the very beginning did not think we would ever find her because he said she was at the point of impact,” said Jeanne. “‘She was vaporized,’ he said.”Jill’s husband, Steve Campbell, was a Police Department officer.

He visited his young son at the Maurers’ house, and Jeanne and Joe thought Steve would take Jake home once he had his bearings. When it became apparent to the Maurers that Jake would remain with them, they moved their grandson’s bassinet upstairs from the living room. What had been Jill’s childhood bedroom would become Jake’s.

In many ways, he had a typical and happy upbringing, raised in a middle-class neighborhood. There were Little League games. Visits to Santa’s Village.

Catholic school. Church on Sunday — and Mets games, the family’s other religion. Still, Jake told me recently, “It was sort of unavoidable that something was off.” He felt an emptiness. “The person that brought me into the world — the reason I existed, the anchor to my own existence — just was not there,” he said. “It’s hard to describe the strangeness of the feeling.”In a nightly bedtime ritual, Jeanne and Joe would hand Jake a framed photograph of his mother for him to kiss.

Among his earliest childhood memories is the feel of glass against his lips. The medical examiner never identified any remains as Jill’s, so ground zero became the cemetery the family visited every Sept. 11 and on Jill’s birthday in June. Like most curious children, Jake had many questions.

But he often was afraid to ask them, not wanting to see his grandparents sad. One day when he was 4, he summoned his courage and approached his grandparents about the woman in all the pictures: Did my mom talk? Jake pored over Jill’s scrapbooks and family photo albums. He watched grainy VHS tapes, like the one with Jill swaying with baby Jake in her arms at his baptism, with the Lee Ann Womack song “I Ho...