DETROIT — It was a typical frigid winter night in this city, only now a historic blizzard was on the way. Robert Jones Jr., homeless and jobless for more than a decade, calculated his next move.

This 62-year-old resident of Detroit’s North End knew the slice of pizza he had just been given by a store clerk would not last. He needed some quick cash. So on his way home he detoured down familiar railroad tracks, looking for the industrial junkyard where for many years, he said, he could grab loose pieces of metal to sell, usually without repercussions. Yet within minutes, his instincts started to speak up.

“Something in the back of my mind said, ‘Get out of here,’ ” recalled Mr. Jones, who had been arrested in this yard six years earlier. Too late. Security guards stopped him, and the police came. And as had happened before, the only metal he left with was a pair of handcuffs slapped to his wrists.

For generations, scavengers have prowled this city with impunity, pouncing on abandoned properties and light poles to pilfer steel, copper and other metals they could trade for cash at scrapyards. The practice left tens of thousands of buildings so damaged that they could not be restored, turning places like the North End into grim cityscapes that appeared to have been ravaged by a tornado.