A family member of a slain victim mourns after arriving at the Imam Ali mosque, the site of a suicide bomb attack, in the village of al-Qadeeh in the eastern province of Gatif, Saudi Arabia, May 22, 2015. A suicide bomber blew himself up at the Shi'ite mosque in eastern Saudi Arabia during Friday prayers, residents said, killing around 20 people and wounding more than 50, local residents and a hospital officials said. REUTERS/Stringer 

Family members of victims and well wishers are seen after a suicide bomb attack at the Imam Ali mosque in the village of al-Qadeeh in the eastern province of Gatif, Saudi Arabia, May 22, 2015. A suicide bomber blew himself up at the Shi'ite mosque in eastern Saudi Arabia during Friday prayers, residents said, killing around 20 people and wounding more than 50, local residents and a hospital officials said. REUTERS/Stringer 

Family members of victims and well wishers are seen after a suicide bomb attack at the Imam Ali mosque in the village of al-Qadeeh in the eastern province of Gatif, Saudi Arabia, May 22, 2015. A suicide bomber blew himself up at the Shi'ite mosque in eastern Saudi Arabia during Friday prayers, residents said, killing around 20 people and wounding more than 50, local residents and a hospital officials said. REUTERS/Stringer TPX IMAGES OF THE DAY

Family members of victims and well wishers are seen after a suicide bomb attack at the Imam Ali mosque in the village of al-Qadeeh in the eastern province of Gatif, Saudi Arabia, May 22, 2015. A suicide bomber blew himself up at the Shi'ite mosque in eastern Saudi Arabia during Friday prayers, residents said, killing around 20 people and wounding more than 50, local residents and a hospital officials said. REUTERS/Stringer 

Family members of victims and well wishers are seen after a suicide bomb attack at the Imam Ali mosque in the village of al-Qadeeh in the eastern province of Gatif, Saudi Arabia, May 22, 2015. A suicide bomber blew himself up at the Shi'ite mosque in eastern Saudi Arabia during Friday prayers, residents said, killing around 20 people and wounding more than 50, local residents and a hospital officials said. REUTERS/Stringer