Details of the bombers who carried out the Easter Sunday terror attacks in Sri Lanka, killing 359 people, are slowly coming to light. One of them is believed to have been “well-educated” and studied in Britain and Australia before coming back to Sri Lanka to carry out the attacks. “We believe that one of the suicide bombers studied in the U.K. and later did his postgraduate in Australia before coming back and settling in Sri Lanka,” said Ruwan Wijewardene, the state minister for defence. Eighteen suspects were arrested overnight, bringing the total number behind bars to 58. However, prime minister Ranil Wickremesinghe warned that several suspects—including nine directly linked to the attack—were still at-large.

President Maithripala Sirisena has called for a massive security overhaul and ordered the resignations of two of his top security officials, who ignored a number of warnings that the bombings would occur—including one that came just hours before the attacks. Another lawmaker has suggested that the two officials should be arrested and prosecuted, The New York Times reports.