Separating Christian students from their Muslim classmates, the raiders killed 147 and wounded dozens more.
Three months later, the survivors' physical wounds may have healed, but the trauma they experienced continues to affect their lives -- and those of everyone around them in Garissa.
Iqra Abdi Haji, 21, was in her first year of an economics degree at Garissa University when the school was attacked. A practicing Muslim, she was caught in the gunfire and shot in the shoulder; her friend Zeynab was also seriously injured.
"I vividly remember. It was 5.47 a.m. when I realized things were not the way they were usually. We didn't have water, there was no light -- it was a blackout in the school.
"I woke for prayers. After the prayers I went to the bathroom ... some of my friends didn't make it to the bathroom. That's when I heard the gun shots."
Haji and Zeynab tried to run away. As they raced past the university cafeteria, Haji realized she was bleeding from several wounds. Despite their injuries, the pair managed to get to the university mosque.
They and seven other students hid in the mosque, and were able to call for help.
"There was this man that came into the mosque. He was KDF [Kenyan Defense Forces]; we thought that [he was] Al-Shabaab coming to kill us. We turned our backs -- we know they shoot you in the head. We thought it would be better to be shot in the back than in the head."
Haji says she has found it hard to get used to normal life again. "Life was full of trauma."
But after counseling from the Red Cross, which Haji says "encouraged" her to return to her studies, she and her friends have been transferred to Moi University, where they are now living together in dormitories again.
"I thought that I could never continue my studies and that it will end here, but now I think that I'm someone and I'm heading somewhere. I want to be somebody in life."
Joseph Alessandro, Bishop of Garissa
Maltese priest Joseph Alessandro, now the Bishop of Garissa, came to Kenya in the early 1990s.
He was shot by separatist militants on the Kenyan coast in 1993, and left the country to receive medical attention, but he was determined to return. He eventually came back to Garissa five years ago.
In spite of the threats that arrive like clockwork before every Sunday mass, he says he would never consider leaving his congregation.
"It's not a matter of choice," he says. "It's our duty to remain here. Since we are appointed as bishops, we have to stay -- not withstanding what happens -- 'til there are no Catholics, it's our duty to stay."
In the wake of the attack, he says, many students stopped attending their classes.
"Before the Garissa attack, we had 460 students in our school. After the attack, only 300 reported back. The others left Garissa or were scared to come back [to school] because of the attack."
Alessandro says he hopes that the institutions forced to shut down because of the threat of terror will soon reopen and that life will return to normal.
"Now we are gaining confidence again -- we have security on the compound for the school and even during the night for the sisters, for the priests."
Mohammed Hussein, student
Mohammed Hussein was a student at Garissa University when the deadly attacks took place in April.
More than three months on, he is still in limbo -- classes at the college have yet to resume.
"The teachers said they will not return because of the insecurity, because of what happened here," he told CNN, standing outside a locked classroom at the university.
While many of his classmates have transferred to other institutions around the country, Mohammed is one of a group of 60 students yet to be relocated.
For now, he is very uncertain of his future.
Sister Everlyn Ingoshe, nun in the diocese of Garissa
Sister Everlyn Ingoshe, 41, works at Garissa Cathedral's school, having devoted her life to working with children.
She says she knew the risks of living and working in a region where Christians have suffered many attacks.
"I knew that there was a danger in coming to this part of the country for a non Muslim, but I followed my heart, and wanted to do it."
And despite the risks, she is determined to follow her faith.
"If you can go your place of work, you can also go to a place of worship."
Abdelrashid Bare, brother
Abdelrashid Bare's brother Hamza, 26, disappeared thee months ago, just days after the Garissa University attack.
Bare has CCTV footage from the telecom shop where Hamza worked, showing him being handcuffed and taken away by armed men who the family believes were Kenyan police officers.
He has not been seen since.
"I feel a lot of pain," says Bare. "Al-Shabaab killed one of my brothers, and the government took my younger brother. We don't know where to run."
Their mother, Maryam Mohammed, a 68-year-old Somali Kenyan, says: "We just heard the boy was taken away.
"It's the Kenyan security officers. One guy ran after them and reached them at a petrol station, but they pointed a pistol on him and was ordered to go back. We are not aware of any crime he committed."
Kenyan Interior Ministry spokesman Mwenda Njoka said that while he was not familiar with the case of Hamza Bare, Kenyan prisoners were not held without a fair trail or being charged.
"The law requires that you are not held for more than 24 hours before you are brought to court ... nobody is supposed to be held for longer than necessary. We don't have detention camps here."