airtight alibi

Translations
железное алиби
He had an airtight alibi for the night of the crime.
У него было железное алиби на ночь преступления.
Definitions
An airtight alibi is a defense or explanation that is so strong and convincing that it cannot be disproven or challenged, often used in legal contexts to prove that a person was not present at the scene of a crime.