IT WAS JUST THERE. Dawn broke on January 1, 2001, and from a patch of frosted grass in Magnuson Park that had been bare the day before rose a nine-foot-tall slab of steel. No plaque at its base, no markings on its cold, smooth surface—nothing to betray its creator. Was it a heavenly transmitter? An interstellar Trojan horse? Seattleites were stumped, reporters from across the country—and around the world—called the park’s staff for comments, and for two days the hulking hunk of metal pulled gawkers close, as if it had tapped a subterranean vein of postmillennial zeitgeist. And then it was gone.

What became known as the Seattle Monolith—a reference to the enigmatic monument in 2001: A Space Odyssey that inspired it—turned out to be of terrestrial origin, and the guerrilla artists who conceived it fessed up years ago. But a decade later there are as many questions surrounding the gray giant as when it appeared. For starters, it didn’t just vanish from the park. It was stolen. And some of its makers still think it was an inside job.

Caleb Schaber, a Ballard-based artist and frequent attendee at the annual Burning Man festival, helped install the steel behemoth, and when it mysteriously showed up on Duck Island in Green Lake days later, he came forward to claim it. His public admission hacked off his fellow pranksters, who’d hoped to remain anonymous, and today some suspect he staged the theft to keep the story—and himself—in the papers. “He swore up and down that it wasn’t him,” says Chris Lodwig, who conceived the Monolith project with two friends, Eric Leuschner and Titus Grupp. “But if I were a gambling man, I would say he had something to do with it.”

Even if Schaber didn’t steal the Monolith, he may have been indirectly responsible: He allegedly bragged to friends that he’d hidden something inside the hollow structure before it was planted in Magnuson Park. Leuschner suspects it was work stolen from another artist, who then stole it back, along with the Monolith. (Grupp knows what the mystery object was, but he’s not talking: “Considering [Schaber’s] love for media attention, the fact that he never made public hiding anything makes me think he wanted it to remain unknown.”)

Sadly, what Schaber stuffed into the Monolith and the part he played in its theft may remain a mystery. He took his own life in spring 2009 after returning home from Afghanistan and Iraq, where he’d been embedded as a photojournalist; even if he lifted the ’lith, no one’s holding a grudge today. “He was an enigmatic figure, to put it mildly,” Lodwig says. “I wish you could talk to him.”