The masked gunmen first ordered the Christians travelling to the Egyptian desert monastery to get down from the buses they were in -- and then to recant their faith.
The mix of faithful visiting the sanctuary along with monastery workers refused.
And one by one, the gunmen, who had lain in wait for the convoy to appear, shot them dead, killing 29 people.
Friday's horrific attack on Egypt's Coptic Christians, claimed by the Islamic State group, has further devastated this ancient community, coming on the heels of two church bombings in April that killed dozens.
IS had threatened further attacks, but while police boosted security around churches in the country, no one was prepared for a strike on the desert road leading to the Saint Samuel monastery in the southern province of Minya.
The jihadists appeared to be in no hurry as they perpetrated the massacre, according to a priest and a relative of one survivor.
"They told the men to disembark from the bus, took their identity cards and the gold they had on them, and asked them to the recite the Muslim profession of faith," said Maher Tawfik, whose niece survived.
"They took gold jewellery and money from the women, as the children hid under the seats," he said.
The victims, many of them found were sprawled dead in the sand, appeared to have been forced to kneel before being shot in the head, Coptic priest Hedra Rashid said.
"They asked them one by one to deny their Christian faith, but they all refused," said Hedra, who spoke to survivors.
In the small town of Bani Mazar, not far from the scene of the attack, grieving Christian women in black veils could not hold back their tears at a ceremony to mourn the dead in Saint Mark's Cathedral.
The minority, roughly 10 percent of Egypt's 90 million people, has been under assault for months.
Before the April bombings, an IS suicide bomber had attacked a Cairo church in December, killing 29 people.
In Sinai, where the jihadists' Egypt franchise is based, a wave of murders of Copts has forced dozens of Christian families to flee the peninsula.
The latest blow to the Copts, coming in Minya, was especially difficult.
The Christian minority is especially well established in the conservative province, and for decades tensions had occasionally flared with their Muslim neighbours.
In 2013, after a police crackdown killed hundreds of supporters of ousted Islamist president Mohamed Morsi, Muslim mobs attacked several churches in the province.
Islamists accuse the Copts of supporting Morsi's overthrow by the military, although the Muslim religious establishment and opposition groups also backed his ouster.
"It is not new for us to be targeted by terrorism. We pay the price for supporting our army and state," said Mina al-Masri, who had come to attend the funeral of a friend's relatives killed in the attack.
"I expect a bloodbath against Christians in the coming period," he said.
Others shared his sense of foreboding.
"There's no surprise, just pain," said Mina Said, 35. "It hasn't even been 50 days since the (church) double bombing."
Hanan Fouad's neighbours, a family of six, were killed in the attack.
In the cathedral courtyard on Saturday, she simmered under her transparent black veil.
"It's going to happen again. Not a month goes by without them killing Christians," she thundered.
"Why the Christians? Because they say we are a minority, that we're infidels."