Earl Melchert did not plan to be home on the afternoon of Sept. 5. He was supposed to be at work managing a fertilizer plant in a town in western Minnesota.

He returned briefly because he had forgotten a diesel can that he had wanted to fill on his way home, so he could mow the grass that evening. As he prepared to head back to work in Elbow Lake, Minn., about 150 miles northwest of Minneapolis, he looked out his window and saw something moving in his field about a half-mile away.

“I thought at first it was a deer,” Mr. Melchert, 65, said in an interview on Saturday.

What he saw, it turned out, was 15-year-old Jasmine Block, who had disappeared on Aug. 8 from her home in Alexandria, Minn., about 30 miles from Mr. Melchert’s home.

“I could make out her face, and I went, ‘Oh my gosh, this is the gal from Alexandria that’s been gone for 29 days,’” Mr. Melchert said. “It’d been on the news, it’d been online. It went national. It was on posters, in stores, her face, her picture. Right away I recognized her.”