(CNN) -- After a series of raids, police made new arrests in the public stoning death of a pregnant Pakistani woman, bringing the total of people in custody to 12.
Farzana Parveen, 25, was killed in Lahore last month because she married a man against her family's wishes.
The latest arrests include her two brothers and her ex-husband.
The mob of 28 people that attacked her included members of her immediate family, authorities said.
Shortly after her death, police arrested five people, including her father, her uncle, two cousins and the driver who brought the relatives to Lahore.
The court is treating the death as an act of terror that has "wider consequences on the safety and well being of all of society," according to lawyer Maliha Zia of Aurat Foundation, a Pakistani women's rights organization.
She said she was worried that international pressure may have forced the government to convene an anti-terrorist court in an act of "show and tell."
Pakistani police officers will be investigated because they didn't intervene when Parveen was publicly beaten to death with bricks, a court official said.
Such killings not uncommon
Such killings often originate from tribal traditions in Pakistan but are not a part of Islam. They usually happen in rural areas, not large cities such as Lahore. Human rights activists said bystanders, including police, often don't intervene because the killings are considered family matters.
The Human Rights Commission of Pakistan said 869 women were victims last year in the nation of about 180 million people.
Women's rights advocates say the actual number may be much higher. The United Nations estimates that at least 5,000 women worldwide die yearly in such killings.
The prevalence of violence against women in Pakistan became apparent when Parveen's husband, Mohammad Iqbal, revealed to CNN that he killed his first wife six years ago so he could marry her. His son said Iqbal served a year in prison.