More than 500 men and women died in honour killings last year, the Human Rights Commission of Pakistan says. Many of these crimes, carried out by relatives who say their mostly female victims have brought shame on the family, are never prosecuted, observers say.
Police named the suspect as Muhammad Asif, saying he has been on the run since Tuesday night, after murdering his sisters Fozia Bibi, 22, and Suriya Bibi, 24, in the eastern province of Punjab.
"Muhammad Asif killed his two sisters last night over their character and lifestyle, which he didn't like," police officer Tariq Mehmood told Reuters. "Fozia was shot in her chest and Suriya was shot in her waist."
Police said neighbours and relatives had told them the deaths were honour killings, over Asif's suspicions that his sisters were having affairs.
Police said Asif was jailed after having murdered his mother four or five years ago, but set free after being pardoned by his family, but declined to provide details.
Pakistani filmmaker Sharmeen Obaid-Chinoy won an Oscar on Sunday for a documentary about honour killings, prompting activists to call for changes in laws to punish those who kill women deemed to have disgraced their families.
Pakistani law allows criminal cases against those charged with a killing to be dropped if the families of their victims forgive them, or accept a "blood money" offering instead.
The forgiveness option in the law can effectively waive a complainant's right to seek the punishment of the accused, even in the case of attempted murder.
Changing the law to remove the possibility of "forgiveness" could help cut the number of honour killings in Pakistan.
Domestic abuse, economic discrimination, honour killings and acid attacks make Pakistan the world's third most dangerous country for women, a 2011 Thomson Reuters Foundation poll showed.
