Another survivor, Arslan Yousaf, shed more light on the attack.
He said as soon as the blast happened, armed men charged into the train and started firing at people.
"They had launchers, guns, and other weapons," he said. "They kept shouting, 'We will kill anyone who doesn't come out.'"
Yousaf also recounted how they were segregated according to their identities - Punjabis, Baloch - and attacked separately or in groups.