Justice Secretary Leila De Lima said Tuesday investigations indicate Alpha Phi Omega was responsible for blasts at La Consolacion College, the University of Perpetual Help and near De La Salle University, the Philippine Daily Inquirer reported.
The National Bureau of Investigation has determined the explosions at La Consolacion College in 2008 and at the University of Perpetual Help in March were "connected" to the bar exam blast near De La Salle University on Sept. 26, De Lima told a news briefing.
She said the motives behind the three attacks were "similar" but declined to say if they involved a frat war.
The NBI has charged one APO member in the September exam blast.
De Lima said leaders of the fraternity are not cooperating with investigators.