Ishtekhar flew into a rage and throttled his 17-year-old sister after finding her making love to Irfan in the early hours in Kheri Shikohpur village, police said.
After throttling his sister to death, Ishtekhar went to the house of Irfan, who had fled from the scene, and fired at him with a country-made pistol, they said.
But the bullet missed the target and hit Irfan's uncle Bhoora in the abdomen wounding him seriously, police said.
Ishtekhar had been taken into custody, they said.
