Irma González recognized the gray backpack in the photo. It was the same one her son had used for high school and the one he had taken with him for his first job three years ago, just before he vanished.

When Ms. González, 43, saw the images on television of bone fragments and scattered personal belongings uncovered on a ranch in western Mexico, her heart sank. Had her son, Jossel Sánchez, met his fate there? Were his remains there somewhere? Or had a criminal group brought him to that place only to take him elsewhere?

Standing about 300 feet away from the entrance of the Izaguirre ranch on Wednesday, surrounded by sugar cane fields and barren hills, she was desperate for answers.

“I just want to find my son, dead or alive,” she said while sobbing and pleading with local police officers who had cordoned off the site to let her inside.