INDIANAPOLIS, Oct 8 - More than 200 people, many wearing white as a sign of peace, gathered on an Indiana university campus on Wednesday to pray for an American humanitarian worker held hostage by Islamic State militants. Abdul-Rahman Kassig, formerly known as Peter Kassig, 26, was threatened in a video issued last week by Islamic State militants that purported to show the beheading of British aid worker Alan Henning, 47. Kassig had been a student at Butler University in Indianapolis, where nearly 250 people gathered in prayer with his friends and his parents, who did not speak to the crowd. Many in the audience wore white as a sign of peace as speakers talked of Kassig's humanitarian efforts and the plight of those he was helping Syria before his capture. During the vigil, Hazem Bata, the executive director of the Islamic Center of North America, asked Kassig's captors to have mercy on him "and be warned that God also said he who kills a soul unjustly will be as if he killed all humankind." Kassig's parents have said through a spokesperson that their son was doing humanitarian work through an organization he founded to treat refugees from Syria when he was taken captive on Oct. 1, 2013. Kassig converted to Islam while in captivity and has adopted the name Abdul-Rahman, the family spokesperson said. Henning's beheading, condemned by British Prime Minister David Cameron and U.S. President Barack Obama, was the fourth such killing of a Westerner by Islamic State, following the deaths of two U.S. journalists and another British aid worker.