に違いない

に違いない expresses a strong belief that something is certainly true, with the nuance of strong certainty or conviction based on evidence or reasoning. It is used when the speaker is almost certain about the reality of a situation and wants to assert it confidently. It often appears after a noun, a verb in dictionary form, or a noun/na-adjective phrase that serves as the basis for the conclusion. Examples: あの人が犯人に違いない。 That person must be the culprit. この証拠から彼は犯人に違いない。 From this evidence, he must be the culprit.