Why do you think Jane was crying ?

Holden never finds out exactly why Jane cried, except that he felt as if it had something to do with her step-father.

"I asked her, on the way, if Mr. Cudahy--that was the booze hound's name--had ever tried to get wise with her. She was pretty young, but she had this terrific figure, and I wouldn't've put it past that Cudahy bastard. She said no, though. I never did find out what the hell was the matter. Some girls you practically never find out what's the matter."