Replace `has happened' by `had happened’.

The error is in part (2) of the sentence. The correct sentence should be "The victim tried to tell us what had happened but his words were not audible." Here's the explanation:

The sentence is in the past tense because it refers to something that happened in the past. The verb "tried" is in the past tense, so the verb that follows it should also be in the past tense. The verb "has happened" is in the present perfect tense, which is not appropriate here. The correct verb to use is "had happened," which is in the past perfect tense.

The past perfect tense is used to describe an action that was completed before another action in the past. In this case, the action of "what had happened" was completed before the victim tried to tell them about it.

Here are the definitions of the tenses used in this sentence:

• Past tense: Used to describe an action that happened in the past.
• Present perfect tense: Used to describe an action that started in the past and continues up to the present, or has just finished.
• Past perfect tense: Used to describe an action that was completed before another action in the past.

Here's the corrected sentence with the relevant tenses highlighted:

"The victim tried to tell us what had happened but his words were not audible."

In summary, the error in the sentence is the use of the present perfect tense instead of the past perfect tense, and the corrected sentence uses the past perfect tense to describe an action that was completed before another action in the past.