Just looking at news clippings, Portland-area problems at the suburban stations seem to be related to perpetrators who live within a mile or two of the station. The exception was a drug-dealing problem at the Lloyd Center stop which has been mostly cleared up. Gangbangers can no longer afford to live in downtown or inner Northeast Portland.
Another issue is large noisy groups on trains at night, though I often ride the eastside line around 11 p.m. and this seems to happen mostly near the weekends, during festivals, or in really warm weather. A modest patrol presence would make a difference.
Tigard, on the other hand . . .