The son of Muhammad and Nazo Afzal, Asif, saw his sister, Sumera, in an intimate circumstance with cousin Zeeshan and became enraged. Asif suspected for a while that his sister was having an affair with cousin Zeeshan and, seeing them together, he decided to do something about it. Asif grabbed a gun and shot Sumera in the head.
Don't think that the murder had anything to do with the fact that Zeeshan was Sumera's cousin. It had everything to do with Sumera bringing dishonor on the family.
Marriages to first and second cousins are more common than non-cousin marriages in Pakistan. I have relatives there who've married their cousins. It brings a whole new meaning to the phrase "all in the family."
Pre-marital sex or necking, even with a cousin, could have serious and, as we've read, deadly consequences. The situation is not much different for extra-marital sex or even suspicion of it. For example, in Iran women found guilty of adultery are stoned to death. Most of the Muslim world has a noxious mix of the state and the family suffocating the lives of women. Many women don't have a say in their marriage. It's usually the elders in the family who decide upon the choice of a "perfect" husband.