KARMALAHANG, India—When the call came from New Delhi, Punita Devi braced herself for the worst. Her husband, she learned, had been sentenced to death by hanging.

Akshay Kumar Singh and three other men were convicted this month of a crime that focused the world's attention on violence against women in India: the gang rape and killing of a 23-year-old physiotherapy student on a bus in December.

For...