Most of the 147 victims of a terror attack on a Kenyan university on Thursday died execution-style as they lined up waiting for their turn to be shot, a senior Kenyan government source has told The Telegraph.
Some students were killed as they spoke to their parents on the telephone, having been ordered to call with messages from the gunmen that their aim was to force Kenyan troops to leave Somalia, the source added.
"This is the level of depravity that we are dealing with, it is something beyond the comprehension of anyone normal like you or I," the source, who spoke anonymously, said. "These are not people who can be reasoned with, only force can stop them."
The suicide vest-clad gunmen, whom the Somali terror group al-Shabaab claimed as their own after they stormed Garissa University in northeastern Kenya, also told students they were "here to make your Easter holidays better" and warned of further attacks to come, survivors revealed.
Maureen Manyengo, a 21-year-old Christian from western Kenyan who was training to be a teacher, described how she hid inside her wardrobe after seeing several friends killed.
"I could hear the attackers telling my friends, 'Do not worry, we will kill you, but we will die too'," she said.
She said the terrorists also told the cowering students: "We are not bad guys, we are just here to make your Easter Holiday better."
Reuben Nyaora, an aid worker who was among the first to enter the university after the terrorists' final clash with Kenyan special forces late on Thursday afternoon, described seeing women rise from among the corpses covered in blood but unscathed.
"I have seen many things, but nothing like that," said Mr Nyaora. "There were bodies everywhere in execution lines, we saw people whose heads had been blown off, bullet wounds everywhere. It was a grisly mess."
So far, 147 people have been confirmed dead and 79 injured in Kenya's worst terror attack for two decades, but officials have admitted that the death toll could climb higher still as piles of bodies are recounted.
Meanwhile, questions remained about how the 15-hour siege reached its final bloody end and how the death toll jumped from 70 in the late afternoon to 147 just over an hour later.
Kenya's interior minister confirmed the gunmen had been strapped with explosives and blew up "like bombs" as they were shot by an elite special forces squad.
The Telegraph's government source said that when the squad reached the room where the attackers were holed up, they had just six hostages with them, whom they killed. They then denoted their vests as they died in a hail of bullets, the source added.
At the gates of Garissa University, soldiers kept large crowds of sobbing relatives at bay as inside, the bodies of those killed were recounted.
"I am so worried, I had a son who was among the students trapped inside the college, and since yesterday I have heard nothing," said Habel Mutinda, an elderly man, his face streaming with tears.
"I tried to identify his body among those killed. I have to do that before the body goes bad in the heat. I have been camping overnight. It is really hard, it hurts."
The gunmen targeted Christians over Muslims according to al-Qaeda guidelines the terrorists who attacked the Westgate shopping mall in Nairobi two years ago also followed.
One witness described how they headed directly to a lecture hall where Christian students had gathered for an early morning prayer session.
Another told how Muslim classmates tried to dissuade them from their murderous spree, but were ordered to go to the college's mosque where they were told they would be safe from harm.
Kenya's government, which has faced criticism for its failure to act on intelligence to combat threats, said it would not be "intimidated or humiliated" by what happened.
"The government is determined to fight back the terrorists, and I am confident we shall win this war against our enemies," said Joseph Nkaissery, the Interior Minister.
World leaders offered their condolences and renewed pledges of support to the Kenyan government in tackling the terror threat. Pope Francis said in a statement he would pray for a "change of heart" by the terrorists.
"In union with all people of good will throughout the world, His Holiness condemns this act of senseless brutality," The Vatican said in a statement.
Questions are now being asked about how the authorities reacted to intelligence that an attack was imminent, potentially on a university, and whether it has learned lessons from its haphazard response to the Westgate attack, in which 72 people died.
Peter Aling'o, senior researcher with the Institute for Security Studies in Nairobi, said al-Shabaab was taking advantage of "gaps" in Kenya's intelligence-led security planning.
"I think Kenya hasn't learnt anything at all in terms of how to respond to terror attacks," he said. "What we are seeing is a knee-jerk reaction that sends in security personnel in a manner that suggests they are not completely aware of what they are responding to."
Some of those who escaped Thursday's massacre said posters had been put up around campus and the university's administrators warned about an imminent attack but they were "ignored" or dismissed as an April Fool's prank.
"Yesterday there were those notices, but as it was April 1, we just thought that it was fooling," a student named only as Katherine told AFP.
Students from a nearby teacher training college said they too had been warned that "strangers" suspected to be terrorists had been spotted in Garissa in the days leading up to the attack. As a result, their college was closed and they were sent home.
Five people have been arrested in connection with an attack, CNN reported on Friday evening, citing Joseph Nkaissery, the Kenyan Interior Minister.
He added that the university would be able to confirm on Saturday whether everyone had been accounted for.