The reason the investigators are mad at the coroner is because he is releasing information they could use if and when a perp is ever caught. Questions such as those below could be used to validate whether this person was actually there or not, and it is also information that only the cops and the perp himself would know.
1) What happened that morning when Officer Gliniewicz began to approach you ?
2) Was there a struggle between the two of you, and where did it happen exactly?
3) Did you shoot him ? How many times did you shoot him ? Who's gun did you shoot him with ?
4) How many shot did you fire ? How many shots hit him ? How close were you to him when you pulled the trigger ?
5) How did you manage to get hold of his gun ? Did your friends help you ambush him ?
6)Which way did you run after you shot him ? Where did you throw the gun you shot him with ?
7) Did you grab him by the arm, hand, neck, head, leg, etc ??........(For DNA matching )
8) What kind of shoes did you have on ? What about your friends, what were they wearing ?
9) How did you leave the scene, walking or driving ? What about your friends ? How did the three of you get there that morning ?
Every one of these questions are questions that the cops may know the answer to and the perp(s) would also know. The perps are the only ones that would know these answers for a fact. LE can match up his answers to verify if he was really there or not. If this information makes it out to the general public, than just about any clown out there could claim to be the shooter based on what he read in the newspaper.
It's that kind of information they fear will be leaked out by the coroner and "jeopardize" things for them.
I understand their frustration to some degree, but I also understand that completely shutting out the public is a huge mistake. All that does is fuel rampant speculation of exactly the kind we are seeing here. They should and could release certain information that would help shore up the public's confidence that this story actually happened the way it was told in the beginning. For instance, just step forward and say "We have undeniable PROOF there were three unidentified persons at the scene with Gliniewicz that morning." Period. They really don't need to offer much more than that, and could still retain plenty of "secret evidence" for their interrogation process.
That statement in itself would be good enough for most people. LE won't do that though, which is the entire problem. There are many things they could tell the public in order to dampen speculation and stop the rumors, but for some reason they have chosen not to. Due to this information "blackout", the public is feeling as though they are being lied to and shunned, and apparently so is the coroner himself.
If they have absolutely no proof that these three people ever existed, then that is going to be a whole different ball game. Personally, I think they probably do, but any and all information pertinent to that evidence is being withheld, even from the coroner.
It's a swampy area. What's in a swamp ? Mud, sand, dirt. If you have three sets of footprints at the scene besides Gliniewicz, then release that information. It wouldn't jeopardize anything, and it would go a long way in shutting up all the armchair detectives.