Mexican gangs, like all gangs, only attack when they know they’re stronger and think they’re safe. And on a US Army base, they wouldn’t be.
Also, gangs are motivated by money and not ideology. They’ll go along with anybody who pays them enough.
So therefore, if you’re thinking suicidal ideologically motivated attack, I’d say there’s only one group left...
According to Twitter, per NBC, Feds originally thought these were military, but are not sure about that now.