If someone commits robbery, the police don't say we can't investigate the crime because someone committed murder and that's far more important.
Someone doesn't take the 5th because there isn't anything to investigate. Christie should have found out what was going on at the very least. Instead he kept making fun of the scandal. This has been going on for months now. He could have already found out what was going on at the bridge and what were the details of the so called traffic study. Instead he claims ignorance and he says he didn't ask Bridget why she lied because he wasn't interested by the time he fired her.
Are you really worried that this incident will not be thoroughly investigated?
This will be the most investigated event since the Kennedy murder (one of the ones where a Kennedy died, not one of the ones where a Kennedy killed).
The state police, the FBI are already on the case. Plus every single journalistic manhour possible will turn over every rock, scan every computer, sniff every crotch they have to uncover every last shred of evidence they can. And, even then, if they find nothing implicating Christie in the event, they'll declare him guilty simply because the preponderance of investigative effort proves he was involved.
Someone doesn't take the 5th because there isn't anything to investigate.
Christie didn't take the fifth. He answered questions from the hostile press for over an hour. One of the guilty parties pleaded the fifth, no doubt under orders from his lawyer.