First off, do you have a link about the grandmother/granddaughter who were shot with an "assault rifle" ? Quite often the press will sensationalize a story. I'm not doubting you, I'd just like to read the story to give it a reality check.
As to what to do, well simply be aware, be aware of your surroundings, be aware of ambush points, and be aware that if you are too focused on being aware to the crime potential then you soon will no longer be aware of the enjoyment of riding your bike, so be aware of staying aware of your cycling. Some people get so focused on the dangers of riding in traffic that they no longer enjoy riding and give it up because it is too dangerous.
There is a rail-trail near where I live that goes through a section of trees away from the roadway and any houses, fairly well secluded. There is also a county jail just down the road where there are a lot of work-release inmates. The county jail also acts as a holding facility for some Federal prisoners for the Illinois based Federal court system. So, basically, anyone on the trail could be a recreationalist, another cyclist, or someone convicted of drunk driving who is using the trail to go to work or back to jail, or someone visiting a higher profile inmate and who didn't want to park on the courthouse property due to a variety of potential reasons. So basically anyone I encounter on that trail section, especially at night, could be anyone from "nothing to worry about" to "someone you don't want to run into in a dark alley" . So I just avoid that section of trail at night by taking a mile detour to the main roadway that parallels the trail. Daytime no problem, nighttime I take additional precautions.
And do take note as someone above suggested of neighboring areas that the trail passes through. But beyond that try not to worry too much about it, make some adjustments in your route at different times of day, and carry on. Quite often the worry about a criminal is out-weighed by the soccer mom who was paying more attention to her kids in the backseat than on the road ahead, and not to single out soccer moms because any driver can be distracted and inattentive distracted drivers are a graver concern to cyclists than random criminal behavior and criminal activity in a particular area. It's the ones you don't see, and the ones who don't see you, that end up getting you.
Have a good ride, be aware, stay safe, but do try to enjoy the ride. Life is too short to be in a constant state of fret and worry.
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Life happens, don't be a spectator.