What did the 'One terrible long-drawn cry' suggest

When Jim gets close enough to hear, he realizes that Silver is trying to persuade a man named Tom to join the pirates. Their conversation, however, is interrupted by an angry cry in the distance and then a scream, something that Jim recognizes is a death cry. Alan, another honest sailor, has been killed by the pirates because he will not convert to their cause. Tom starts to walk away, but Silver reacts very angrily, throwing a tree branch at him which makes him fall to the ground. The one-legged Silver, devoid of his crutch, is still able to swiftly move to Tom and stick him with a knife not once, but twice.