All,or most of the original 4 murders and a suicide,are held under PII,so we'll never know and it's not fair really as no reason has been given for their " secrecy".
Could have been a bit of envy going on that others hadn't been there first ( looking for promotion,or hanging on to their jobs because of the Diane Jones case ) where the higher-ups had been seething at the incompetence of the force.