I'd agree with you that not saying anything is the right move if he was involved in the murder or knows what happened, but if he is innocent then I disagree.
How could it hurt him in court if he truly is innocent? If he's innocent he should tell the police he's innocent and knows nothing, he should tell the public he is innocent and knows nothing, and if he ends up in court he should tell the court he is innocent and knows nothing. I can understand the first day when the cops knocked on his door for him to say he wants his lawyers present, but now this is 5 days in and he still hasn't said a word? If knows nothing about the murder it would help him more then hurt him right now to say so.