On November 24, 2017, a bomb ripped through a mosque in Egypt’s northern Sinai region as terrorists opened fire on those finishing Friday prayer at the al-Rawdah mosque. The attack killed 305 people—including 27 children—and wounded 120, in what was the deadliest terrorist strike in the country’s recent history.

The bloody attack was a cruel turning point for the country. While attacks had been common since 2013, when the current president overthrew President Mohamed Morsi of the Muslim Brotherhood, targeting mosques is rare in Egypt. Terrorists had previously attacked Coptic Christian churches and security forces, but generally avoided Muslim houses of prayer.

This mosque was made up primarily of Sufi Muslims, a mystic sect of Islam that strives for direct personal connections to God. They are hated by ISIS.

The attack occurred just days before the prophet Muhammad’s birthday, when the mosque was packed with worshippers. Suddenly, 25 to 30 militants pulled up in four off-road vehicles. They fired on worshippers from the mosque’s main door and 12 large windows. Adding to the horror, several bombs and rocket-propelled grenades went off as worshippers tried to flee. The gunmen set fire to cars parked outside the mosque and shot at arriving ambulances to hinder escape.

While no group took responsibility, evidence pointed to ISIS. In an interview published in an Islamic State magazine, a commander in Sinai outlined the group’s hatred for Sufis and identified al-Rawda as a target.

In an address given on television, Egyptian President Abdel Fattah al-Sisi vowed that the government would respond with “brute force.” Security had been a key reason for his supporters to back him, and with a possible re-election on the horizon, retaliation was expected.

Hours after the attack, Egypt’s military launched air strikes on targets in mountainous areas around the city, and three days of national mourning were declared.