The incident took place late Monday in Serchhip district.
"R.C. Lalchuangkima after returning from the forest, kept his bullet loaded hunting gun in his home Monday night. His son John Kennedy reportedly used the gun to shoot his elder brother David Lalengzuala, who died on the spot," a police officer said.
Kennedy pumped two bullets into his 12-year-old brother's head, said the officer. Police are yet to ascertain the motive behind the killing.