Yap.Town

を疑っていた

was doubting; suspected

→ を
phrase Rare #32,663
was doubting; suspected Used with を to say that someone was doubting or suspecting a person, claim, ability, action, or alibi. The ending ていた indicates an ongoing or habitual state in the past.
JA: 彼は私の説明を疑っていた。
EN: He doubted my explanation.

警察は彼の行動を疑っていた。

The police were suspicious of his behavior.

トレンブレーを疑っていたアフリカから

From Africa, who suspected Tremblay

— 教皇選挙 (2024)

彼女は夫の能力を疑っていた。

She doubted her husband's ability.