He was convicted of second-degree arson because the fire started accidentally.

second-degree 是由 second（第二）和 degree（等级）组成的复合形容词，在法律术语中表示"第二等级的"或"次级的"。 second-degree arson 指"二级纵火罪"，通常指非预谋的纵火行为，比一级纵火罪（有预谋的纵火）情节较轻。