[aohige]

Here's your answer. I posted this over at AP.

one of the Himajin pics:
Ivasan: Let's release him, Mugiwara boy. He would be a powerful addition to us.
I know you won't stop now... especially if you intend to go to Marine HQ!!
Luffy: Huh, Iwachan!! But this guy did....!

Crocodile: Ivankov...!!!

Ivasan: Long time no see (rest cut off)
Luffy: You know him!?
Ivasan: Yes, long time ago... When he was still just a rookie!
Don't worry, even if he does betray us, I'll keep him down. We can't trust him, but...
I'm holding a "weakness" of his! I'll keep my mouth shut, if he agrees to lend us just his power!
Crocodile: damn you....!!!


There you go, for those who were debating on Croc's betrayal.
Croc's motive to get out of the prison, is becase he wants to go after Whitebeard.
Also from the last panel:
Jinbei: I won't let you go after old man Whitebeard, Crocodile...!
Crocodile: Or what, you wanna fight to the death right now?