The police inquired into the case. (Passive Voice)

The case was inquired by the police

The case is inquired by the police

The case should be inquired by the police

The case will be inquired by the police

All of the above

Past Indefinite Tense

Active formula: Subject + past tense form of the verb + object

Active: The police inquired into the case.

Passive formula: Object of the active sentence + was/were + past participle form of the verb + by + subject of the active sentence

Passive: The case was inquired by the police OR The case was inquired into by the police.