I live "in the area", so to speak, of where this happened and know the woman who made the facebook post that is linked in the original post as well as her husband. I do not know them well enough that I can just call them up and start peppering them with questions. Our relationship is that of a casual customer/business owner type. But I have known them for long enough to know they are of a fine upstanding type. I would be more then happy to have them as neighbors or have them watch my kids.
I can reasonably guess where this happened as she and her husband own a little bit of land that they live on that borders an irrigation ditch, as well as the other participants in the rescue, are sons of farmers, or they themselves farm nearby.
I do not know the Irrigation district employee who shot the elk and cannot vouch for his character or lack thereof.
Water to irrigate the farms around here is delivered via a series of ditches and reservoirs that stretch from Grand Coulee Dam south to just North of Pasco . These ditches are either constructed of dirt, rock or in the case of where this happened apparently concrete. Google things like "Elk or Moose trapped in ditch in Pasco or Eltopia" etc, and you will see that this is an almost yearly occurrence that an animal gets trapped in one of these ditches lately. Outcomes are mixed. I've had two dogs drown in these ditches when they cannot climb back out.

Roads run along these ditches. Irrigation district employees drive on these roads to deliver water to farmers who order it the day before. Farmers also use these roads to access fields/homes etc. The ditch and the road are BLM run. Thus in the pictures of the guy butchering the Elk, the animal is laying in this BLM road. This road is NOT for the publics use, but rather for the farmers who own or farm the farms that border it. However, bird/coyote hunters will drive these roads hunting. Sometimes the farmer cares and will run them off, other times they do not care. Quite often the hunters think they have a right to drive these roads to hunt because its BLM, maybe they do, but as soon as they take fives steps off the road they are on the farmers land.
From what I gather from the FB post, the rescuers called the Irrigation district to let them know of the elk stuck in the ditch. The elk can die in the ditch, get washed down and stuck in a pipe or block a grate. Thus the ditch might overflow and wash out the banks. So not only is it a case of feeling bad for the animal, but there is also the very real chance that there could be a failure in the ditch.
In the mean time , as farmers do, instead of waiting for someone else to do the job, and having equipment to perhaps get the job done, they get the elk out. Per the fb post, a district employee or employees show up after the rescue has been completed, says good job guys and thankyou for getting the elk out. All is good, the rescuers bring some hay and grain for the elk and plan how they will help the elk out overnight. Meanwhile, it sounds like if you read Maryjos fb post, the guy(s) who went to the rescue site who work for the irrigation district goes home, tells his wife or kids about the neat rescue, the people involved and where it happened. Then, the relative of the district employee, thinking this is a neat story, shares it on FB. "Evil Jim"

who works for the irrigation district but is off work sees the post, loads his kid in his pickup, drives to the elk and shoots it from "4 feet away" on the last day of the season in his gym shorts, Saturday September 19.
What I do not know:
-Was any of the rescuers actually there when the elk got shot or did they show back up after it had been killed? It sounds like from the FB post that they were there to witness the kill as they report that the elk stood and was shot from a distance of 4'.
-Did the district relatives fb post go into any description of the circumstances of the elk ending up where it was? This is a moot point if the rescuers were there when he shot it as they would have told "jim" of the rescue and there intent to help the elk out overnight from coyotes.
-Did the district worker who shot the elk cross private land on a farmers road to access the elk or did he turn off the county road and wind his way to the elk on the BLM road?
-If the district employee who shot the elk was off work and used the BLM road, is he trespassing because he did not use the road in his work duties but rather as a private citizen like you and I
Like any court case that I have been a juror on, the lawyers will talk of "reasonable assumption".
If I find out more I will post.