What causes johnny and ponyboy to come back to face the police? (the outsiders)

I said we're goin' back and turn ourselves in," Johnny repeated in a quiet voice. I was surprised but not shocked. I had thought about turning ourselves in lots of times, but apparently the whole idea was a jolt to Dallas. "I got a good chance of bein' let off easy," Johnny said desperately, and I didn't know if it was Dally he was trying to convince or himself. "I ain't got no record with the fuzz and it was self-defense. Ponyboy and Cherry can testify to that. And I don't aim to stay in that church all my life."

Summary: johnny wanted to turn himself in and tell the police that it was self defense. Besides, he didnt wanna stay in church forever.