Who was the murderer?

Hint 1 of 9:

Whoever the murderer was, he seemed interested in those Venus de Milo
statues that everyone was buying.

Hint 2 of 9:

He broke several of them open to see what was inside them.

Hint 3 of 9:

The De Vries diamonds were never found.

Hint 4 of 9:

And the murderer must have been someone who knew to look for them.

Hint 5 of 9:

He must be one of the original thieves or someone who talked to him.

Hint 6 of 9:

You can rule out Nat Cook -- he's still in jail.