Saudi Arabia's religious police are being blamed for the death of two sisters who were murdered in what is known as an 'honor killing' by their brother after the sisters were arrested for allegedly mixing with unrelated men. The Society for Defending Women's Rights in Saudi Arabia said the religious police arrested the two sisters, aged 19 and 21, thus putting their lives in danger. Their brother shot them to death in front of their father when they left a women's shelter in Riyadh on July 5, according to Saudi news reports. The practice known as honor killing is a daily occurrence in Saudi Arabia. The incidents are staged to look like a suicide or an accident, Wajeha Huweidar, a Saudi women's rights activist told The Media Line. "This case is shocking, because it didn't occur behind doors. It happened in a public place and was published in local newspapers," she said. Huweidar said the Saudi government was in denial of the honor killings trend and doing nothing about it. The Commission for the Promotion of Virtue and the Prevention of Vice, otherwise known as the kingdom's religious police, was criticized for arresting the girls, which sparked the brother's anger and led to their deaths. "I think the religious police had a big role in this crime and many other crimes," said Huweidar. "When a woman gets arrested for mingling with a non-male relative, that means her life is ended. She gets to go to a prison or to a women's shelter and her family will not come to pick her up. The Saudi male guardianship system doesn't allow women to be released without the presence of their male guardian." "The hands of the religious police as well as the brother's hands are stained with the blood of these innocent young women," the Society for Defending Women's Rights in Saudi Arabia said. "These women have not committed any crime deserving to be killed in such a brutal way." Honor killings - cases in which women are killed by relatives for socializing with men who are not their husbands or relatives - are a common practice in the Middle East and governments are trying to use legislation and awareness campaigns to end them. Saudi Arabia, which is governed by a strict form of Islamic law, does not allow women and men to mix if they are unrelated. The religious police enforce this and other religious rules, such as an Islamic dress code, prayer attendance and prohibiting possession or consumption of alcohol. The women's rights organization called on the Saudi authorities to charge the brother with murder and bring members of the religious police involved in the girls' arrest to justice. The religious police have come under fire over the past few years for their strict and sometimes brutal clampdown on what is perceived as un-Islamic behavior, fueling international criticism against Saudi Arabia's human rights record. Earlier this year, Saudi King Abdullah Bin Abd el-Aziz initiated sweeping reforms, including firing the head of the religious police. It is thought that the reforms were an effort to moderate the country's leadership and present to the West a more toned-down image of the Saudi kingdom. Saudi Arabia is an ally of the United States in the war against terror, but it has come under international pressure due to its strict religious practices. Restrictions in the kingdom are particularly harsh for women, who are banned from driving and cannot perform most tasks outside the house without being accompanied by a male guardian, usually a husband, father, younger brother, son, or other close family member.