Nairobi - A survivor of the Garissa attack and hostage situation says he heard al-Shabaab militants call out Christians before shooting them.Collins Wetangula, who is also the vice chairperson of the Garissa University College students union told News24 that he heard the attackers question students whether they were Christian or Muslim before attacking them.He said he heard gunshots and when he looked outside the window, he saw masked men shooting. He then locked fellow students in his room and sat tight."They were shouting loudly that they are al-Shabaab and that that we should all be afraid," he said of the beginning of the attack.There could be many deadHe added that students were afraid to scream for help as it alerted the attackers to their presence.It is then that he heard them ask students to say Islamic verses before shooting those that did not."We were sure they would get to us, that is then that Kenya Defence Forces KDF officers arrived through a back window and evacuated us," he added.Wetangula said he suspected that many students could still have been caught up in the melee and that he feared there could be many casualties."There are usually many students in the hostel compound. As many as 700, there could be many dead, I hope not," he added.So far, police have confirmed that 17 people have died in the attacks and that 535 students are yet to be accounted for.