Screenwriting : Truth is stranger than fiction by Jeff Zampino

"Based on", "Loosely Based" "Inspired by" all have different heaviness when coming to adopting real event into story or script. Either way this needs to be mentioned clearly at the beginning of the script in all due fairness and respect toward the reader. Too many films these days cheat on "real events" to gain bigger exposure or infamousness. But I do agree truth can be often stranger than fiction and I think in your case the absurdity of the event can be even mentioned in your opening.

I agree, I would either use "Based on true events" or "Inspired by actual events with names and places altered to protect the identity of those concerned." Alternatively you can do what the late Michael Crichton did, which was "This book contains information, which if revealed, would be a violation of the official secrets act, hence for all intents and purposes, this novel is a work of fiction, and any resemblance to actual facts, events places or persons living or dead is purely coincidental and non-intentional."#

Inspired by usually means loosely based. Is there a reason you want to avoid using a super in the beginning? There are clever alternatives to the obvious..for example "Truth Is Stranger Than Fiction. Then dissolve to or add specific date. You can also structure your script so it feels real because it contains a fair amount of roughly historical info or events. Think about Once Upon A Time In Hollywood. Title and ending aside, so much of script based on actual events one might easily assume story was true. There are other devices or creative executions you can consider as well, including but certainly not limited to the use of dates and times or executing with documentary or news-like aspects in part or throughout.