What do you think is the biggest art scandal in the past century?

Richard “Rick” Abath, the guard who opened the door to two thieves who robbed Boston’s Isabella Stewart Gardner Museum of masterpieces worth more than $500 million in 1990, died Friday at his Vermont home, according to his attorney.

Abath steadfastly maintained that he played no role in what remains the largest art heist in history and one of Boston’s most notorious unsolved mysteries. Yet, he remained under intense scrutiny over the decades by federal investigators who never ruled out the possibility that the thieves had help from someone with inside knowledge about security at the museum.