The school in Yobe, one of three Nigerian states under a state of emergency since May as killings have left hundreds dead, was unguarded.
But the armed men weren't there to offer protection. They entered dormitories and began firing in the dark, killing more than 40 students.
"At first we thought they were security personnel on surveillance," one student said.
"They had uniform like that of the Army," added Musa Bade, a teacher. "They did not talk to anybody."
Bade described the terror as men on seven motorcycles and two vans approached the College of Agriculture in Gujba and opened fire.
The attackers were suspected of being Boko Haram, a militant group whose name translates to "Western education is forbidden." The group is known to attack schools, including one in July that killed 42 students.
"Why did they kill them? You can ask and ask," Nigerian President Goodluck Jonathan lamented in a televised address Sunday. He instructed the country's security chiefs to "look at different ways of handling" the violence.
More than 4,000 people are thought to have been killed in four years of the conflict.