Does anyone believe and entity could murder a human being?

I don't believe that an entity as you put it could kill someone directly. Through fright or flying debris is yet another story. IMHO

If the spirits energy is high anougth then i think it could, but what are the chances of that?

Depends which theory of the paranormal you subscribe to really.
If you believe spirits are just psychic projections then no.
If you believe in a sort of afterlife where people's spirits become good or evil then yes.

Many many theories out there. I think, in the sense of a poltergeist, where the energy builds up and starts going postal, inadvertently, a knife may accidentally fly into your stomach.

My uncle was damn near strangled to death by his own pentacle. I was nearly smothered by something on my chest and it happens quite often. Granted, not usually by ghosts but they can do it. Remember the phenomenon known as hagging? If it isn't psychosomatic (which I don't know if it can be entirely) entities kill people quite frequently.

I think It woud be difficult for an entity to commit murder, they are basically just energy which needs someone to channel. Now the idea of the power of suggestion to cause someone to commit murder while believing they were being controlled by an entity, I believe is very possible. These are the basics of the voodoo/voudon religion x

I remember when I was six years old, waking up to a GHOST that was coming out of the closet at my mom's house one night, after waking up from a deep sleep. I jumped out of bed and came back and it was gone. A near GHOST experience gone in a flash.