Disoriented and distressed, Hayat Khan sits in a Karachi jail thinking of the day he murdered his sister to protect his family's honour.

"She used to talk to a boy over the telephone," the 20-year-old says from his cell.

"I asked her many times not to talk to the boy, but she refused and finally the same boy came to our door, which made me crazy."

Following tribal tradition and goaded by his cousins, the young man was convinced it was his duty to kill her.

"My cousins said what a dishonoured man I am that my sister is talking to a boy over the telephone," he says.

"She was bringing a bad name to our respectable family."

Warning: this story contains graphic images.

His family comes from the Swat Valley in northern Pakistan, and lived under Taliban control until the Pakistan Army launched a scorched-earth offensive against the militants in 2009.

Displaced by the war, they moved to Karachi, bringing with them the strict tribal traditions that guided their life.

In the city he was confronted by a Pakistan that's starting to change its attitudes to women, and a Government taking bold steps to stamp out honour killings.

Hayat Khan killed his sister Sumaira, 16, for talking to a boy and "shaming" the family. ( ABC News: Asif Hassan )

Children discovered his crime

It was Khan's young neighbours who discovered his crime.

The children were playing cricket barefoot in the dirt street of their Karachi slum when they heard screams and shouting from one of the houses and rushed over.

"We peeped inside and we saw our neighbour, Hayat Khan, was carrying a long knife and was beating his sister," says 11-year-old Nawaz.

"He was abusing her in their Pashto language."

Khan was stabbing 16-year-old Sumaira in a frenzied attack, and deliberately cut her throat.

"There was blood all around and she was twitching," recalls Nawaz.

Watched by neighbours who alerted police, Khan dragged his seriously injured sister outside the house, then sat beside her body and checked her mobile phone.

Nawaz, 11, was playing cricket when he heard screaming from a neighbour's house and investigated. ( ABC News: Amar Guriro )

Murderers walk free after paying blood money

Until recently, perpetrators like Khan were mostly pardoned for murdering women to protect the family's honour.

Under Islamic law — the Qisas (an eye for an eye) and Diyat (blood money), which was introduced by military dictator General Zia ul-Haq in the 1970s — the killers walked free after paying a small amount of blood money to the victim's family.

This loophole was tightened in October by the Government after global outrage over the killing of social media starlet Qandal Baloch, whose brother is charged with her murder.

Honour killers like Khan now face a life sentence, with a minimum 12-and-a-half years' jail.

But beefing up the laws has not stopped the practice; nearly 40 honour killings have been recorded since then.

Killed for marrying for love

Barely three weeks after the law changed a Karachi couple were murdered to save a family's honour.

A still from the mobile phone video showing Sumaira after her brother's fatal attack. ( Supplied )

The woman, named Irfana, had divorced her first husband and shamed him and his family by marrying another man — for love.

The lovers' fate, like that of many victims of honour killings, was decided at a Jirga, a traditional men's council.

Despite being illegal in Sindh province, and ignoring the newly strengthened laws, the Jirga met in a private Karachi house. The chieftain issued the verdict: Irfana and her new husband, Asmat Khan, must both be killed.

"Irfana's brother tied her and Asmat with ropes, and her former husband Nizam strangled both of them to death and secretly buried the bodies in a local graveyard," says senior police officer Javed Akbar Riaz.

Police arrested the six men who attended the Jirga, but the law makes no sense to them.

"She is married to me, how can she even think to marry someone else when I am alive," says Nizam from his prison cell.

"I could have been left feeling guilty my entire life if I let her go."

Those who migrate to Karachi brought tribal traditions, including honour killings. ( ABC News: Amar Guriro )

Society's mindset needs to change

The practice is widespread. Male family members kill women for talking to a male stranger, for dressing immodestly, marrying according to their own will, or for defying basic Islamic teachings.

Abdul Hai from Pakistan's human rights commission says new laws will not stop honor killings. ( ABC News: Amar Guriro )

Last year 1100 cases of honour killing were reported, but the Human Rights Commission of Pakistan (HRCP) estimates at least another 1,000 went unreported.

Many people feel it will take a lot more than laws to put a stop to the practice.

"We need to change the mindset of the society," says Abdul Hai from the HRCP.

Fundamental grassroots change supported by the government is needed, according to leading voice for women, Dr Nadia Agha from Shah Abdul Latif University in Sindh.

"We have to empower women through education and employment. The stronger the bargaining position they have, the more capable they are to fight and survive," she says.

Dr Nadia Agha believes a policy of grassroots social change is the only way to stop the killings. ( ABC News: Amar Guriro )

Dr Agha argues it is critical that men are involved in social change at the village level.

"If we do not sensitise men, then it won't work," she says.

"Currently, even if women want to report a crime, they can't go outside without men's approval and without a male chaperone."

For now Khan and others who are caught will pay a price, but are confused by the rights and wrongs of their actions, and which authority is greater: Islamic customary law, or the Government.

"It was so sad, I didn't intend to kill her, just wanted to frighten her, but accidently she was killed," Khan says with tears in his eyes.