No one knows for certain what happened, but it's a fair bet that it was not an accident.
没有人知道究竟发生了什么,但几乎可以肯定这并非意外。
Dressed in dark glasses and old clothes, they had taken special precautions so that no one should recognize them.
他们戴着墨镜,穿着旧衣裳,特别小心以防别人认出他们。