[mrsmith]

Gangs or cartels tend to act ‘for effect’. Professionals do as you said.

[kabar]

Be very surprised if it were gang related with an attack at a government facility. Dressed in black with masks and possibly bulletproof vests. Sounds like a description of the Paris attackers if you substitute suicide vests for bulletproof vests.

They obviously wanted to get away and survive. The fact that you could assemble three people or more to participate in a massacre does suggest terrorists or gangs. I tend to the former rather than the latter.