Twins?

So, just as I was deciding that I would stop trying to figure out who the killer was, she throws me a bone.

The death count is up to three. Mrs. Roberts went to sleep and never woke up, casting doubt on both her husband and the doctor who gave her a sleeping drought. Then the General was struck down by a blow to the head. He had gone a bit strange before that though so I think something else was going on there.

But the bottom line is that I had no idea who could possibly be the killer. I was just as confused as the people on the island.

Oh but then...

Three of the men, while searching the house, see the butler, through a window, heading out to serve drinks. Seemingly moments later, they run into him in the attic gathering his clothing to move to another room. Then, later, when being questioned, he had a slight cockney accent that he had not had before. I believe there might be two of him. I think he has a twin. The only question is, why did he gather these particular people to kill?