Great Expectations.

Okay, so in chapter 5, pages 34-36 the sargent discovered the two convicts. The book said that one convict was yelling murder and that the other convict was trying to kill him. My question is why would the convict try to kill him? When the soldiers were holding them hostage, "Pip's" convict was exclaiming how he helped the other guy and so why would he try to murder him. He is saying how the other guy is evil and he didn't do anything. Why would "Pip's" convict try to kill him... I don't know wether it was just so he could keep hiding and he wouldn't have to worry about bein caught if the other guy was found or because Pip ran into him or something song those lines.
From the several pages:
"Tried to murder him?" said my convict disdainfully. "Try, and not do it? I took him, and giv' him up; that's what I done. I not only prevented him getting off the marches, but I dragged him here-dragged him this far on his way back. He's a gentlemen, if you please, this villain. Now, the Hulks has got its gentleman again, through me. Murder him? Worth my while, too, to murder him, when I could do worse and drag him back!"
When Pip was first telling the convict how he had run into another man who he thought he was, the convict seemed really confused and kinda iffy on hearing about how there was another guy around the marches. Now he is stating how he helped his guy all the way through their escape and how he is a villain and a liar... I'm jus so confused. Help would be nice(: Thanks!