A 9/11 street teacher at the scene of the crime
The passengers from New Jersey spill out of the train station and across the blistering sidewalks of Lower Manhattan, oblivious to one another as they steamroll toward their destinations.

One rider stands out from the pack: a broad-shouldered man wearing jeans, T-shirt and a baseball cap, a tattered gym bag slung over one shoulder. He takes in the scene outside the station, at the edge of the former World Trade Center, and homes in on a young couple.

"Do you know the past? That's the question I ask!" he barks cheerfully at the pair, who have no time to respond before he fires off his next question.

"Where are you from?"

"Uh, L.A.," the man says slowly, clearly trying to decide whether this sweaty interloper — Harry John Roland — is nuts or nice, a tour guide or a bum, but also drawn in by his wide grin and giddy demeanor.

Roland follows up with the same obscure detail he shares with everyone he meets on these streets: the exact time it was in their hometown when that first plane hit the World Trade Center on Sept. 11, 2001.

In Los Angeles, it was 5:46 a.m.

The couple listen and nod as Roland begins reciting the history of the fallen buildings. They sidle away after about 30 seconds, but Roland isn't fazed. He moves on and keeps on talking — bellowing actually — a singsong phrase that is nearly as familiar in this neighborhood as the clangs and drones of heavy machinery inside the construction zone known as ground zero.

"History, don't let it be a mystery!" Roland shouts to nobody in particular. "How many buildings were there before they were gone? Don't get it wrong! Don't say two, 'cuz that's not true!"

In the 10 years since 9/11, the site has become a magnet for tourists and for entrepreneurs hawking postcards of the twin towers, books of photos from the day of the attacks, and key chains with American flags.

For Roland, it has become an obsession and a public stage. He is a tour guide of sorts who works for nobody but himself and is paid in tips stuffed into a plastic jug that hangs from a strap around his neck. He's known as "the World Trade Center man."

Every day, he appears outside the disaster site to talk about what happened to the buildings and the people inside them, to lovingly wipe down the plaques honoring fallen firefighters, and to badger tourists into asking him questions and listening to his hypnotic spiel.

"Don't be scared — say something!" he belted out to a family who stared back, wide-eyed and silent, when Roland challenged them to recall how many planes were hijacked that day. The answer is four. But a decade after the fact, memories are fading, laments Roland, who says he is driven by a preoccupation with the towers and a determination to make people — particularly Americans — learn from history and cherish what they have.

"America is appreciated only when you leave it," said Roland after greeting some tourists from Israel.

"I don't have to tell you about terrorism," he told them. "Americans have no idea."

Although he shouts, "History, don't let it be a mystery," more than 100 times a day, Roland's own history is a mystery. This much is clear: He grew up in Harlem, is 57, lives in Jersey City, N.J., and has a 15-year-old son. He says he became a history buff while growing up under the guidance of a strict uncle "who kind of carried the baseball bat in the family."

While other young black men he knew fell victim to drugs and crime, Roland says he learned about history and engineering, though it's unclear whether he ever worked at either. Asked whether he ever lived overseas, Roland says cryptically, "I'm not allowed to say." He gives a similar answer when asked whether he served in the military.

"I wish I knew more about him," said Robert Maxwell of North Carolina, who met Roland when he and his wife visited the World Trade Center site after the 2001 attacks. They were captivated by Roland's mix of street theater and history lectures and have stayed in touch. Maxwell described Roland as a "troubled soul," driven by something that only he understands.

"He's just got this thing pushing him," Maxwell said. "He doesn't seem to have a political agenda. He just knows everything about the towers."