MANILA - The University of Santo Tomas (UST) Faculty of Civil Law has suspended classes on Sept. 21 and declared it a "day of mourning and prayer" following the hazing death of its freshman Horacio Castillo III.

"Dean Nilo Divina has declared Thursday, September 21, 2017 a Day of Mourning and Prayer. There will be no classes in the Faculty of Civil Law," The Jvstinian, the law school's official student publication, posted on its website.

The announcement came following Castillo's death in an apparent hazing incident involving the school's Aegis Jvris fraternity.

A police autopsy confirmed that the 22-year-old died of a heart attack after sustaining "massive injuries" during initiation rites late Saturday.

Castillo's parents said their son had told them he would attend the fraternity's welcoming rites on Saturday. They were told of his passing before dawn Monday.

• READ: 'Barbaric': Family of UST student killed in hazing cries for justice

On the chair where he usually sat, Castillo's classmates left flowers as they mourned his death.

Upuan ng hazing victim na si Horacio Castillo III, nilagyan ng bulaklak ng kanyang mga kaklase (📸 Sab Borromeo) | via @zhandercayabyab pic.twitter.com/wYC8lGjBzY

— DZMM TeleRadyo (@DZMMTeleRadyo) September 20, 2017

Students also peppered the Aegis Jvris fraternity's bulletin board with colorful notes that decried the fatal hazing and called on frat members to surrender in the name of the law they work so hard to learn.

The Varsitarian, UST's official student publication, released an editorial that criticized the "culture of death" in fraternities.

"What these law students did was unlawful and it stands against kung paano dapat mino-mold ang isang Thomasian," Amierelle Anne Bulan, The Varsitarian's editor in chief, told ABS-CBN News.

Divina, who founded the Aegis Jvris fraternity, earlier visited the wake of Castillo and promised his parents that justice would be served.

The suspension against members of the Aegis Jvris was lifted to allow the frat's members to fully cooperate with investigations.

The Senate is set to launch an investigation into the incident on Monday as Castillo's death revived calls for stronger legislation against violent initiation rites.

• READ: Senate sets probe on fatal hazing of UST student