> Vincennes believed it was shooting down an attacking Iranian fighter
This was due to gross incompetence/negligence. This was a Ticonderoga class frigate equipped with the (then state of the art) Aegis weapons system [1] - capable of knocking down an Exocet missile out of the sky with a hose of lead.
From the linked article:
"The Aegis system was involved in a disaster in which USS Vincennes shot down Iran Air Flight 655 in 1988 resulting in 290 civilian deaths.
It was determined by a formal military investigation[17] that the Aegis system was completely operational and did not have any maintenance problems. The investigation ruled that if the commanding officer had relied on the complete tactical data displayed by the Aegis system the engagement might never have occurred. Additionally, psychological effects of the crew subconsciously manipulating the data to accord with a predefined scenario greatly contributed to the false identification."
Aside from the fact that the captain of the Vincennes was in Iranian waters (without authorisation - and which the US Navy lied about on formal reports), plus the reports of his rising aggression from colleagues working with him, should push this into a military disciplinary matter, along with demotion or discharge.
[1] - https://en.wikipedia.org/wiki/Aegis_Combat_System