The victim was grabbed and pushed outside because he was trespassing.

False : one cannot legally prevent a custodial parent from interacting with the administrative staff of any facility while that facility has custody of that person's child.

Attempting to do so is known as kidnapping.

He was told he was under arrest.

Extremely misleading : he was not at any time under arrest during the actions you describe above.

In fact...

He was forced against the wall, perhaps unnecessarily, perhaps necessarily.

...the statement "you are under arrest" was first uttered while the officer committed several counts of attempted murder by bashing the victims head against a concrete wall.

Being under arrest, he can legally be subjected to a forcible takedown.

False. This is the crime of battery.

In a different case, they might have had a necessity defense against the crime of battery. This is an affirmative defense, not legality per se.

if under arrest, the weapon cannot legally be utilized in any way.

False : bad elk v. us, for instance.

This is also an affirmative defense of necessity (as are all gun acts not involving a safe backstop; it is never per-se legal to kill people, self defense is a necessity defense), and whereas multiple counts of attempted murder in the course of kidnapping occured prior to the felony murder under the qualifying crime of unlawful child kidnapping, executing both cops would have been quite legal under the standard and established usage of the concept of necessity defense, unless it was done after they had stopped their criminal behavior.

The cops were blatantly identified as cops,

This is true; it does not, however, have any legal weight.

did announce the victim's arrest

This is misleading at best, see above. Furthermore, the officer was already committing the crime of attempted murder - a qualifying crime for a necessity defense had he shot the cop - when he made this statement.

In the physical struggle, when the victim pulled the weapon, it justified the first as well as the second (lethal) shot by the cop.

False; while this would have been true in a fairly normal case, felony murder can never be legally justified by a necessity defense, nor by any other measure.

As such, the actions were blatantly and redundantly illegal. (in most jurisdictions, it can also qualify as felony murder from the head-slamming, i.e., attempted murder. oregon, oddly, allows "s/he got violent when I was already committing attempted murder;" it is not a predicate felony. kidnapping is).

In addition to the principle that felony murder can never be legally justified, regardless of the circumstances, it is also the case that premeditated murder can never be legally justified by the circumstances of the immediate moment. The attempts to hoax this man into endangerment, coupled with the ability to politically synchronize his execution with other political violence in the valley, rise to the level of probable cause that the officer committed premeditated murder of this man.

Felony murder. Probable cause to arrest the officer for premeditated murder.

Legally, there is basically no way in hell this police officer did not commit a firmly criminal murder.

I will grant that it might have been a nominally legal, albeit murky,
shooting had the two qualifying paths to felony murder charges and probable cause to arrest the officer for, specifically, premeditated murder not been present. And by "murky," I mean that legally, the deceased would have had the exact same right to shoot the officer, though while physical harassment and battery are considered violent crimes in the state of Oregon, they are not considered felony crimes...

Thankfully, that does not matter worth a damn; the officers' actions redundantly constitute murder (1x felony, 1x premeditated) in a fashion which, legally, cannot be justified by the immediate circumstances.

From the very instant the officer asked the man to leave - the first qualifying felony - that man could have started a mass shooting of the officer, or other students, or anyone else, or done literally anything else, and the officer could not have a legal right to shoot him, literally no matter what. (though others could have, if it rose to "necessity defense" levels) Then, there are the other two ways (the other qualifying felony and the evidence of premeditated murder) by which the officer's actions could never, ever be legal - again, no matter what.

Under law, there is literally no series of events which could have justified any action by this officer which resulted in this man's death, legally speaking. Literally none.

That is the nature of both felony and premeditated murder. Now you know.