I was working in Slovenia in the mid-90s.
I flew with a chap who said he was on this Squadron.
Supposedly its a Yugoslavian Army Gazelle, the base was in Mostar. Event was late 80's.
The crew was indeed killed and the valley this event took place in is now known as "wires valley".
Ive never attempted to confirm any of the above claims but the pilots in the Slovenian Air Force (Bell 412 Sqn) were very passionate about this poster.