Answer:
repression
Explanation:
In psychology, Repression occurs when our brain is trying to protect ourselves from a overwhelmingly painful emotion.
This is what most likely happen to the witness.
The detail of the brutal murder created an intense trauma for the Witness, To protect him/herself, the brain decided 'Repress' / Hide the details of the murder from the memory and made it almost impossible for the witness to testify in the court.
