Riverside Park runs along the Hudson River on New York's Upper West Side. It's a neighborhood gathering place where locals jog or walk their dogs or join in games of pickup basketball. Regulars get to know one another, if only by sight.
In the winter of 2014, park regulars started noticing a man in his early 30s sitting on the same bench every day. He was tall and muscular, with closely cropped hair and a backpack that he always kept by his side. Billy Healey, a local bird watcher, approached him. "It was like pulling teeth to get him to say anything. He was not a talker," Healey said.
