MANILA - The Aegis Jvris Fraternity on Monday vowed to cooperate with the investigation into its alleged involvement in the fatal hazing of University of Santo Tomas student Horacio Castillo III.

"The Fraternity extends its condolences to the bereaved family of Horacio at these very trying times. Rest assured that the Fraternity will extend its utmost cooperation in the investigation of this unfortunate incident," Aegis Jvris said in a statement.

Castillo, a 22-year-old law student, told his parents that he had been accepted to the Juris Aegis fraternity after completing tasks like cleaning hallways and running errands for members. On Saturday, he attended the organization's welcoming rites at the UST campus, his father Horacio Castillo Jr. told ABS-CBN News.

The freshman law student never made it home.

A resident found Castillo's body dumped in a street in Balut, Tondo on the wee hours of Sunday. He was rushed to the Chinese General Hospital, but was already lifeless when he reached the hospital.

His family found him there after receiving a tip from an anonymous text message, his father said.

Autopsy conducted by the police confirmed Castillo died of a heart attack due to "massive injury" consistent with hazing.

• READ: Castillo suffered 'extreme pain' in hazing, says dad

The UST has condoled with Castillo's family, promising to bring to justice those behind the incident.

"We express our profound sympathy and offer our prayers to his family for their pain and anguish--- a pain that we share seeing that the life of our very own student, with all of its aspirations and potentials, taken away because of a senseless act," the Catholic university said in a statement.

"We will leave no stone unturned to ensure that the perpetrators be meted the appropriate sanctions and brought to justice."