Like plenty of other 'white guys' I've been in and around Zamboanga quite a few times visiting family. Luckily I've never had any issue to deal with and never felt threatened despite warnings about how dangerous the area is.
I take care wherever I go in Pinas, even in Manila or Cebu.

Seems this victim was attracting plenty of attention over a period of time.

Yep, I too hope the best outcome will come very soon.