Inspector Will was reading his email, when an urgent message arrived. It was from his friend, Dr. Mallone, the millionaire. It said:
"Hi, Will.
I need your help, you see, somebody just stole one of my pearls.
As you recall, I have a very special chest manually crafted by my old friend Delouresse. It is so exclusive, that he only crafted 3 identical chests before his death. Yes, I'm the proud owner of one of the Delouresse Ebony Chests.
In the chest I was keeping my pearl collar that had exactly 100 perfect pearls. The gold key to the chest I always carry tied to my neck, on a silver chain. I gave a party today, and the chest was in open view because it is a jewel by itself.
Someone then asked me to show her the contents of the little ebony box, and then I tried to open it with the key. To my surprise, the key lock was terribly worn out, like someone was trying to force it. My key got stuck, and I had no option but to break the gold lock. The chest contained my collar, which at first brought relief to my soul. But you know me, I was suspicious, so I counted the pearls twice: there were only 99! The thief managed to open the chest (destroying the valuable lock in the process), took only one pearl, and then closed it. Why?
Please, Will, help me, what can I do?"

Inspector Will searched the Internet about the Delouresse Ebony Chests, and from the page shown, he wrote 3 names. Then he went to Dr. Mallone's house, compared each person on the list with the Doctor's guest book, and found one that belonged to both lists. Inspector Will thinks that person was the thief.
How did he know that? What was the first list? Why did the thief only take one pearl?

Owners of the box...the box was switched..if someone took a pearl the necklace would be broke..an the key didnt work.dunno kinda stumped

I'm stumped

I think one of the other 2 owners switched boxes

you guys got it! :-D

Answer
Another holder of the exclusive Delouresse Ebony Chests put inside his a copy of the collar (but unfortunately for him, with only 99 pearls) and then switched the boxes. The worn out lock was to make believe that a thief broke the lock.
The list Inspector Will took was the one with the names of the proud owners of the Delouresse Ebony Chests. The person in the list and in the guest book then is the suspect.

My dear Watson, The solution is really quite elementary. You see it was Col. Mustard in the kitchen with a carving knife....Oh wait wrong game....sorry Im stumped.