When you place an animal in another animal's territory, and there is no place for them to go, one or the other of them is going to die. Any good habitat for possums already has its fill of possums -- more than its fill. That's why they are under our cars, in our garbage cans, in our yards, in our houses. The animals you transplanted into another's home territory were likely dead within 24 hours -- or else they are back as a nuisance in some other "undesirable" territory under someone's else's house or business.
This is true for rabbits, for squirrels, for raccoons, for possums. Sigh. The whole Havahart thing is really quite a scam.
The intruder to the territory is almost always the one to be killed, as it lacks the home advantage but, sure, sometimes it's the animal already on the territory that is killed. I'm not seeing where any net good has been accomplished.
There needs to more education about wildlife in this country. My friend who has a small acreage in the country has a steady stream of un-informed suburbanites dropping off animals and, no doubt, fantasizing that they will survive. Sigh.
Unless Fish and Wildlife or another licensed, trained agency/person is assisting you in these relocations, you are just contributing to the spread of nuisance animals and, sometimes, disease.
I realize you were trying to be kind, but we have a bad habit of being kind in ways that are ultimately either useless or harmful.
On Edit: Just saw your post where you had assistance from a State Park Ranger -- good, I'm much relieved. Too many people around here are "catching and releasing" at random, I'm afraid. It becomes a sore point.
in most cases an amateur can't throw an animal into a new territory and reasonably expect it to survive