Modal verbs of speculation, deduction, possibility and probability - past

The eccentric inventor ____________________ stumbled upon the solution to sustainable energy in his cluttered workshop

The enigmatic signal from deep space ____________________ been an attempt at communication by an alien civilization

The legendary monster ____________________ been a myth after all, considering the recent unexplained sightings

The experimental drug ____________________ cured the rare disease, but ethical concerns halted the clinical trials prematurely

The elusive dark matter ____________________ interacted with ordinary matter in the ways scientists initially theorized

The dormant volcano ____________________ erupted at any moment, threatening the nearby unsuspecting population

The ancient artifact ____________________ been crafted by a civilization far more advanced than previously thought

The renowned pianist ____________________ performed at the prestigious venue due to an unforeseen illness

The revolutionary technology ____________________ been suppressed by powerful interests to maintain the status quo

The controversial painting ____________________ been a forgery, fooling even the most discerning art experts

The elusive creature ____________________ left footprints in the snow, but the blizzard obliterated any evidence

The ancient artifact ____________________ been crafted by a civilization far more advanced than previously thought

The missing explorer ____________________ survived the treacherous journey through the uncharted wilderness

The supposed eyewitness ____________________ seen the incident from their vantage point, given the obstructions

The forgotten jazz musician ____________________ influenced countless artists, despite his obscurity in mainstream history

The ambitious startup ____________________ revolutionized the tech industry had it not faced unexpected regulatory hurdles

The experimental drug ____________________ cured the rare disease, but ethical concerns halted the clinical trials prematurely

The elusive dark matter ____________________ interacted with ordinary matter in the ways scientists initially theorized

The brilliant mathematician ____________________ solved the centuries-old theorem in a moment of inspired genius

The reclusive author ____________________ intended for her posthumously discovered novel to be published

The extinct species ____________________ possessed remarkable abilities that we'll never fully comprehend

The accused ____________________ committed the crime, as irrefutable evidence places him elsewhere at the time

The ancient city ____________________ vanished without a trace; archaeologists ____________________ been searching in the wrong location all along

The elusive quantum particle ____________________ behaved as predicted in the groundbreaking experiment