what is the motive for killing Turner in Huck Finn

Jake Packard is the man with the gun; he’s trying to convince his buddy Bill to kill the third man, Jim Turner. It seems Jake is afraid Jim will turn on them to the authorities. Jake has a better idea: instead of shooting Bill, they should plunder the rest of the steamboat and then wait for him to drown when the boat goes under. This way, they’ll have clean consciences!