Duke Riddle with 3 suspects

The Duke was known for treating his servants like trash. The maid, the butler, and the cook all hated him. One day, they vowed to get their revenge, no matter the consequence.

Of course, the Duke was unaware of this as he started his day. "Hurry up, I'm hungry." he growled to the cook. He threw his sleeping blindfold to the maid, not bothering to aim, the fabric slapping her face. The Duke picked up the towel offered by the butler, tossing it aside to the ground when done. All three were seething as he left the room.

"Are we really doing this?" the butler asked, picking up the towel.

"Of course." the cook slid tomatoes into the boiling water.

"Understood." the maid folded the blindfold, setting it on the table. "Everyone, get ready. We'll strike when we're all prepared."

The butler went to his quarters, taking out a spool of wire and gloves.

The maid picked an antique gun off the display, loading it.

The cook took a knife from the rack, making sure it was sharp.

?????All three headed to the dining room, as soon as they were done preparing. It took about half an hour for preparations, but all were intent on killing their target.

A few hours later, the Duke was found dead, facedown on the table in a pool of red. The police were called by the servants themselves. However, none of the servants were saying a further word.

"Well, I guess we'll have to get the body to the station and see if we can get more information." the officer on the scene said to the detective. "That's not necessary. I already know who did it." the detective replied. "You're a rookie if you can't find out who." Who was the killer? How did they kill him?