Setting: Well established barn providing lessons to people of all ages of all skill levels

Issue: A gelding that is great for novices thru semi-advanced riders that is aggressive with other horses.

Just for clarity - the horse is not mine nor is the barn mine.

On two separate occasions over the last year the same horse has kicked another horse while in the arena for lessons. The first instance resulted in terrible injuries to the rider of the horse being kicked. The rider on the aggressor was well aware of the possible aggression and was negligent in keeping distance. 

The second occasion took place also in the arena. The aggressive horse was at the mounting block with the rider awaiting help mounting. The aggrieved horse was near but rider had maintained a reasonable distance.  The gelding in question deliberately closed the gap between them and kicked at the horse. Rider fell (status of well being not known to me at this time but presumed to be injured based on description of scene) and the assault had just only begun. Horse 1 chased horse 2 literally in laps thru the arena, with kicks and bites, and even cleared jumps in his path to get to the fleeing horse. He kicked so hard the injured horse was bleeding. 

I did not witness this. It was relayed to me by students present in the ring at the time. Please bear in mind I have zero decision making ability or influence at this barn. 

My thought is this horse should not be used in group lessons. The potential for injuries and trauma is just too great. It is doubtful that he will be retired from the program. 

So my question to you is what do you think you would do if it were your barn, horse or rider on the premises? Do you think this horse can be rehabbed? I have so many questions, thoughts and concerns so... give me your constructive only feedback. I don't need negativity or judgment as I have no involvement personally. I volunteer at the barn for my own enjoyment. 

Scenario for you to consider...