"It's not like getting behind the wheel of a Chevy and pulling away from the curb," he said. "He came almost fully equipped. You know the old saying: If it walks like a duck and talks like a duck, it's a motorman."

Mr. O'Leary said Mr. Thomas had apparently learned enough to operate the train by talking to motormen. Ms. Thomas said her son had also spent hours studying subway manuals, but there was no indication that he had ever driven a train before.

"It is very clear to us he could not have successfully pulled this off without a great deal of interaction with people who know how to operate trains," Mr. O'Leary said. 'A Very Nice Kid'

In the Brownsville neighborhood where the Thomas family has lived since coming to the United States from Trinidad in 1990, Mr. Thomas is known as a nice young man.

"I'm telling you, he's a very nice kid," said Ana Acevedo, who lives in the same block of row houses as the Thomas family and whose son is a friend of Mr. Thomas. "He never got fresh with nobody."

Surprised -- and somewhat amused -- neighbors described Mr. Thomas as large for his age, large enough to seem older if one did not look at his still-boyish face. They said he was polite and kind, uninterested in his classes at Brooklyn Automotive High School but very smart.

"Smart enough to take the train," said one neighbor. Occasional Talk of Trains

Luis Acevedo, 15, said Mr. Thomas had the normal number of friends and talked about the normal things -- girls, basketball and hanging out. Only occasionally did he mention how much he liked trains because they were safer and faster than cars, Mr. Acevedo said.