A few men jumped to the concrete slab of the adjacent building. Leaning against the scaffolding, they reached across the gap to help co-workers make the leap. Women went first. Ms. Rahima made it across. So did Ms. Pakhi. On other floors, people smashed open windows or tore out exhaust fans and leapt into the darkness. Some landed on the metal roofs of nearby shanties. Some landed on the ground.

And some never made it out at all.

Son Phones ‘Ma’ Before Dying

As word spread, people raced to the factory: mothers, fathers, husbands, wives and gawkers. Soon a throng stood beneath the building, their faces glowing in the cruel brilliance of the flames. Golapi Begum left her own factory job and raced to Tazreen Fashions to find her son, Palash Mian. He was 18 and worked on the fifth floor. Ms. Begum stared up at the factory and shrieked.

Then her cellphone rang. It was her son.

“Ma, I have no way to save my life,” he told her. “I cannot find any way to get out. I am in the bathroom of the fifth floor. I am wearing a black T-shirt. And I have a shirt wrapped around my waist. You will find me in the bathroom.”

He hung up. He called his father, as well as several friends. Then his phone went dead.

“I became insane,” his mother said. “I spent the whole night in front of the main gate of the factory. I was screaming all the time.”

She found him the next day. Rescuers had lined up all the recovered bodies on the grounds of a nearby school. Family members unzipped bag after bag, searching. One husband looking in vain for his young wife said the charred human remains looked like chunks of coal.

But Ms. Begum unzipped a bag and found her son. She recognized his face. And he was wearing a black T-shirt.

She collected his body and returned it to their village, where he was buried.