。
The lawyer had doubts about his being not guilty.
Literal
Lawyer [topic-は] his not-guilty [in-に] doubt [obj-を] held.
Notice the kanji choice: 無罪 means 'not guilty' as a legal verdict, distinct from 無実 ('actual factual innocence'). The lawyer's doubt here is about whether the formal verdict of 'not guilty' is correct, which doesn't necessarily map onto the question of factual innocence. In ordinary use the two often blur together, but the distinction is real and the kanji choice matters in legal writing.