Modesto’s father was a veteran of the Philippine-Japanese war, a soldier and a disciplinarian. He served as prison official after the war, thus Modesto spent his growing years in Davao del Norte, where his father worked at the Davao Penal Colony. Modesto’s mother looked after the household and the children.
Modesto was caring and responsible even at a young age. A friend who had been sickly as a boy remembers that Bong, who was younger, behaved like a protective big brother. He liked to look after the underdog. Friends and family called Modesto by the nickname Embong, further shortened to Bong.
An uncle joined the pre-war Olympics as a boxer, so Bong learned to love the sport. Also he liked watching Bruce Lee movies in his free time. He liked to play the guitar. When he started a family, he would sing and play the guitar for his baby daughter.
Modesto taught social science subjects at the Maryknoll High School in Sigaboy, Davao Oriental. He became an active member of the Basic Christian Community (BCC) program in his parish. Through the BCC, he became acquainted with the Federation of Free Farmers (FFF) and Khi-Rho, a movement of young people sympathetic to peasant causes founded in UP Los Baños in the late sixties. At the time Bong joined the Khi Rho, the organization was new in Mindanao. Modesto and fellow youth organizer Eileen, who would later become his wife, helped Khi Rho become established in Davao.
By the early 1970s, Filipinos were restive as a result of the country’s involvement in Vietnam, persistent economic problems, and fears that the country was moving towards dictatorship. Modesto got deeper and deeper into the Khi Rho Movement and the FFF. He became its Mindanao coordinator, and in this capacity, helped organize farmers to join the peasant protests that gained strength towards 1972. Farmers were fighting for tenurial rights, access and titles to their farms, as well as protesting abuses by powerful logging companies operating in their area.
Modesto continued his organizing work with Khi Rho and among the farmers when martial law was installed in 1972, but more clandestinely. By 1976, Modesto and his young family, which then included a daughter and a son, moved to Silang, Cavite. He took a teaching job at the Cavite Institute.
Modesto intended to pursue his political work. He established contacts around Metro Manila and Southern Luzon, and pursued his political organizing as part of the movement to defeat the dictatorship. Eventually, he left his job and became a fulltime organizer.
He disappeared in late July 1977. He failed to return home for his son’s first birthday on July 29. Alarmed, his wife and other relatives, all aware that Modesto was taking huge risks with his political activities, started an immediate search. They visited military camps and went to places he frequented.
Eventually they learned that Modesto was arrested somewhere in the Makati area together with other activists, namely Cristina Catalla, Rizalina Ilagan, Jessica Sales, Ardiana Villaber, Gerardo Faustino, Ramon Jasul and Erwin de la Torre.
Weeks after his disappearance, a newspaper carried an article about an encounter between government troopers and guerrillas belonging to the New People’s Army in Quezon province. The news item listed the names of those slain but the names were obviously aliases. The Sison family sought a permit to exhume the bodies. General Fidel Ramos, then Chief of the Constabulary, gave his approval, and an exhumation of a mass graveyard was performed in Mauban, Quezon, Sept. 28, 1977.
There the body of Modesto, riddled with gunshot wounds, was found with three others. The family took back the body and buried it at the Loyola Memorial Park in Sucat, Parañaque. The following epitaph is written today on Modesto’s headstone: “Buhay inialay sa sambayanan, bunga kalayaan.”