MAYAI LEIKAI, India — A dozen soldiers burst through the front and back doors of a small home here in the middle of a July night, dragged Thangjam Manorama into a room and began to torture her. Her older brother tried to stop them and was badly beaten. Her mother rose to defend her and was knocked unconscious.

After about an hour, Ms. Thangjam was taken out of the house. The next morning, the family found her bullet-ridden body by the side of the road three miles away. Soldiers later claimed that Ms. Thangjam was an insurgent who was shot while she was trying to escape. A medical examiner determined that she had been shot from close range while lying down, that stains on her dress were semen but that multiple gunshots to her vagina made any determination of rape impossible. There was little doubt who was responsible: the soldiers made little effort to hide their faces.

Ms. Thangjam’s death led to months of local protests, including one in which a dozen women stripped naked in front of the local military headquarters carrying a red-lettered banner, “Indian Army Rape Us.” The circumstances of her death were so outrageous that even the prime minister at the time, Manmohan Singh, promised redress.

But a decade later, no one has been arrested or charged with a crime. Activists, lawyers and ordinary people here say they know exactly why: a colonial-era law in effect in India’s periphery that gives blanket immunity from prosecution in civilian courts to Indian soldiers for all crimes, including rape.