In 2008 a complete set of ancient pessoi (glass game pieces) was uncovered from beneath a paving stone in modern-day Israel. Due to their small size, pessoi were easily misplaced, making a whole set a rare find. This has led some experts to suggest that the set may have been buried intentionally; however, without clear evidence, archaeologists are left to _______ what happened.

Which choice completes the text with the most logical and precise word or phrase?