For most runners, the finish line of the New York City Marathon is the end of an arduous journey.

For Gianclaudio P. Marengo, it was just the beginning of a two-day ordeal that ended on Tuesday morning when he was found by an off-duty police officer on the subway — disheveled, confused and still in his running gear.

His race started like thousands of others, on Sunday, in the predawn hours on Staten Island.

Mr. Marengo, 30, does not speak English and had never been to the city, but he was with a team of seven other runners from Italy and he had trained months for this day.

Antonio Boschini, 58, who served as a medic for the Italians, said in an interview that just getting to the race had been a victory of sorts.

Mr. Marengo was part of a group of recovering addicts from San Patrignano, a drug rehabilitation center on the Adriatic coast.