How do the police decide which facts to withhold from the press?
They generally keep quiet about a few details that only the killer could know—anything from an object left at the scene to the way a garrote was tied around a victim’s neck. The chief detective on a case usually decides what evidence to make public and what to withhold, although his choices are sometimes influenced (or overruled) by the police chief. In a high-profile case, the police department will generally hold a press conference immediately after discovering a crime but release few details about the case. Later, once those assigned to the case have had a chance to sift through the evidence, police will decide which details to make public.
It’s not a “matter of public record” when police have to investigate a crime, especially murder.