I was talking about this with friends the other day.
Why the hell would they publicly display the actual jewels in a public display in a museum? You'd think that they would place a set that were indistinguishable replicas that the average person would never know ... hell, even a professional jeweller would need to pick them up and examine them up close with a magnifying lens to identify them properly.
Then take the actual real jewels and store them in a super secure vault underground where only two people are allowed access. Something like ... just place them under so much security and strong storage that no one or very people could have access them them.
It's hard to believe that they would place jewels that are worth hundreds of millions of dollars behind millions of dollars of security behind a glass case. I know the glass case was more secure than that but it was unsecure enough for some idiot to climb in through a window and break open things to get to the jewels.
The only other explanation we came up with is that the heist was organized by the museum or owners themselves as some kind of insurance scam. Everyone always suspects anonymous thieves but seldom suspect the actual owners or museum managers.