I'll give you a lead for this massacre:

The police or NBI need not go far. All they need to do is check all high-school to college aged men from Dasmarinas or Forbes Park. I'm sure their number isn't that significant.

I've observed that well-to-do guys are more inclined to do such petty crimes and misdemeanors than their less fortunate counterparts since they are confident that their wealth and social stature will keep them from the slammers.

Back when I was in college, there was a string of thefts of street signs in Manila. Believe it or not, it was perpetrated by DLSU students and they kept the signs as trophies in their condo. Why would they do such a thing? First, they can. Second, they can get away with it. Third, they needed a good laugh.

I'm sure the guys who killed those cats are operating on the same mindset and are having a good time right now bragging about their latest exploits, even perhaps online. Maybe the police should Google away and monitor local online forums for some guys bragging about it as well.