Why does Long John Silver want to kill the Squire himself?

Long John Silver wants the Squire to lead them to the treasure (he has the map), and even allow them to help get the treasure aboard ship..... but he does want to be the one to kill him..... Silver wants no witnesses.

"Here's this squire and doctor with a map and such--I don't know where it is, do I? No more do you, says you. Well then, I mean this squire and doctor shall find the stuff, and help us to get it aboard, by the powers. Then we'll see. If I was sure of you all, sons of double Dutchmen, I'd have Cap'n Smollett navigate us half-way back again before I struck."

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"But mark you here, I'm an easy man--I'm quite the gentleman, says you; but this time it's serious. Dooty is dooty, mates. I give my vote--death. When I'm in Parlyment and riding in my coach, I don't want none of these sea-lawyers in the cabin a-coming home, unlooked for, like the devil at prayers. Wait is what I say; but when the time comes, why, let her rip!"

"John," cries the coxswain, "you're a man!"

"You'll say so, Israel when you see," said Silver. "Only one thing I claim--I claim Trelawney. I'll wring his calf's head off his body with these hands, Dick!" he added, breaking off. "You just jump up, like a sweet lad, and get me an apple, to wet my pipe like."