1. He had an ace in the hole: an eyewitness. 他手上有秘密武器（神秘王牌）：目击者。
2. The eyewitness can substantiate all the testimony. 目击证人能够证实所有的证词。
3. A 31-year-old man in police custody says he tossed a cigarette out of his car, but an eyewitness told police the man threw a large object, the glass bottle with an accelerant. 拘留在警察局的31岁的一名男子说他从车里扔出了一支烟，但是目击者称他扔出了个大东西，一个盛满了催化剂的的玻璃瓶子。
英英解释
n.
1. a spectator who can describe what happened
2. be present at an event and see it with one's own eyes
