"It was like a giant jigsaw puzzle and the more we started to unearth and peel back the onion of who this guy was and what happened to him in the past and trying to truly understand the reason why he would be so obsessed with a specific case once we start to uncover these things about him we realized that once we explain one set of circumstances we needed to go even further with another set of circumstances."

VOA: standard.2010.02.27

It seems like the moment you begin to look at this question, you were just like peeling the onion.

感觉你们在看待这个,问题时，就像剥洋葱一样。

普林斯顿公开课 - 人性课程节选

And there's a couple others like the "Onion" that are also really big,

还有几家大报纸，像《洋葱报》

旧金山的报纸 - SpeakingMax英语口语达人