PESHAWAR, Pakistan (AP) — Pakistani authorities have arrested four people who allegedly killed an 18-year-old woman in the purported name of honor after a picture of her sitting with a boyfriend went viral on social media, police said Thursday.

The woman’s father and three other men were detained days after the slaying in Kohistan, a district of Khyber Pakhtunkhwa province bordering Afghanistan. Police said they told about the killing on Nov. 24 and officers were still investigating.

According to the local police chief, Masood Khan, the four arrested men apparently killed the woman on orders from village elders, who thought she had brought shame to her family by posing for pictures with a boy.

Khan said the investigation determined that the photo of the couple that went viral had been edited by someone before it was shared on the social media. He said investigators are trying to trace whoever edited and posted the image since it led to her killing.

It was not immediately clear if the photo manipulation falsely made it look like the 18-year-old had sat with her boyfriend.

Khan said the young man in the photo was detained for questioning. He said police also planned to arrest the members of the council of elders that ordered the woman killed.

So-called honor killings are a significant issue in Pakistan, a conservative Muslim country where close relatives take the lives of hundreds of women each year because of actions perceived as violating conservative norms on love and marriage.

Many such killings have been documented by domestic and international human rights groups.

Amnesty International issued a statement Thursday expressing its concerns over the death of the 18-year-old in the Kohistan district. The human rights group asked Pakistan’s government to stop tribal councils from thinking they can order honor killings and escape legal consequences.

“The continued failure of the government of Pakistan to curb the extra-legal power of jirgas, or tribal councils, to run parallel legal systems perpetuating patriarchal violence with impunity is extremely concerning,” Nadia Rahman, Amnesty International’s deputy regional director for research in South Asia, said.

Rahman said authorities must do more than arrest the suspects accused of carrying out such slayings.

“The authorities must end impunity for violence and abolish so-called village and tribal councils that prescribe horrific crimes such as so-called ‘honor killings,’” she said.