That would, IMO, mean that the police and DA believe they have a lock on this. He's either confessed, perhaps implicitly, or made a statement so self-incriminating as to be tantamount to confession. So even if the body turns out to be non-recoverable, Hacking can probably be convicted on the basis of this and the other evidence/testimony alone.
They arrested him because he was going to be released from the hospital..They have evidence in car, apartment and a trash bin(dumpter?)....Took the time to build the case while he was hospitalized.